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Biographical Memoirs: V.59 (1990)

Chapter: Cornelis Bernardus Van Niel

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Suggested Citation:"Cornelis Bernardus Van Niel." National Academy of Sciences. 1990. Biographical Memoirs: V.59. Washington, DC: The National Academies Press. doi: 10.17226/1652.
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CORNELIS BERNARDUS VAN NIEL November 4, I 897—March l O. 1 985 BY H. A. BARKER AND ROBERT E. HUNGATE CORNELIS BERNARDUS VAN NIEL Kees to his friends and students—is best known for his discovery of mul- tiple types of bacterial photosynthesis, his decluction that all types of photosynthesis involve the same photochemical mechanism, and his extraordinary ability to transmit his en- thusiasm for the study of microorganisms to his students. His interest in purple ant! green bacteria developed in his first year as a graduate student. After thoughtful analysis of the confusing literature clearing with these bacteria, he carried out a few simple experiments on their growth requirements. Interpreting the results in accordance with the theories of his professor, A. J. Kluyver, on the role of hydrogen transfer in metabolism, he developer! a revolutionary concept of the chemistry of photosynthesis that was to influence research on the topic for many years. As a teacher he was unsurpassed. Although he taught in a small, somewhat remote institution with modest facilities, the force of his personality, his eloquence and scholarship made the Hopkins Marine Station a mecca for students of general microbiology throughout the western world. EDUCATION AND EARLY LIFE Van Nie} was born in Haarlem, The Netherlands, into a family steeped in a highly conservative Calvinist tradition. 389

390 BIOGRAPHICAL MEMOIRS His father and several uncles were businessmen and did not have a professional education. His father sties! when he was seven years old, ant! thereafter his mother largely depended on his uncles for acivice in educating her young son. Since family tradition decreer! that a son shouIc! succeed to his fa- ther's business, Kees was sent to a secondary school with a curriculum clesignecl to prepare students for a commercial career. At the end of his third year in high school when he was fifteen years old, an event occurred that changed the course of his education. The family was spending their summer va- cation as guests of a friend on a large estate in northern Holland clevotec! to various agricultural activities. A part was set aside for testing the effectiveness of various soil treat- ments on crop production, and van Nie] has described how his host introclucec! him to the methods of agricultural re- search and how impressed he was to learn that "one could raise a question and obtain a more or less definitive answer to it as a result of an experiment . . . particularly because ~ hac! grown up in a milieu where any kind of question was invariably answered by the stereotyped reply: 'Because some- bocly (usually a member of the family) said so"' (1967, I, p. 2~. Van Niel's interest ant! enthusiasm for these activities lect his family to reevaluate his education, and he was finally al- lowed to transfer to a college preparatory high school. Uncler the influence of one of his teachers in the new school he developed a strong interest in chemistry. He liked analytical chemistry so much that he set up a small laboratory at home and analyzed samples of fertilizer in his spare time. His aca- clemic record in high school was sufficient to obtain acimis- sion to the Chemistry Division of the Technical University in Delft on graduation without taking the usual entrance ex- · — amlnatlon. He entered the University in autumn 1916 but, after only

CORNELIS BERNARDUS VAN NIEL 391 three months, was incluctect into the Dutch army, in which he server! until the end of December 1918. Life in the army was both a traumatic and a highly educational experience. Removed from the protective environment of his family for the first time, he was exposed to the rough and impersonal life of military training. He later wrote that up to this time he tract been "utterly unaware of the many problems to which man is exposed and with which he must learn to cope." For- tunately, he receiver! practical and intellectual support from a former high school classmate inclucted at the same time, Jacques de Kacit. After a few clays in a primitive military camp on the out- skirts of Amersfoort, Jacques proposer! that they rent a room in the city where they couIct spend their free time in greater comfort. They were soon joined by a friend of Jacques, ant! the three comrades spent their leisure hours discussing many subjects. Jacques was an intellectual with a cosmopolitan background. He introduced van Nie} to new worIcis of liter- ature, art, ant! philosophy. Under his influence, van Nie! read many of the works of Zola, Anatole France, Ibsen, Strinct- berg, Shaw, and Nietzsche. Their ideas frequently conflicted with van Niel's Calvinist background and lee! to what he later described as the rebellious phase of his life. On returning to the University after army service, van Nie! was undecided! whether he should continue the stucly of chemistry or take up the study of literature. But, discussing the alternatives with an aunt whose judgment he trusted "at least in part because of her unconventional attitudes and be- havior," he was finally persuaded to continue on in chemistry. Still, his mental turmoil was such that he could not immecti- ately switch back into the normal academic routine. He spent the first six months reacting French, English, Scandinavian, and Russian 19th century literature ant! was not prepared to take the first year chemistry examination in June 1919.

392 BIOGRAPHICAL MEMOIRS In the autumn, however, he finally settled down to serious study and by intensive effort was able in June 1920 to pass both the first- ant! second-year chemistry examinations. Dur- ing the following year, van Nie! took several courses in biol- ogy in addition to the prescribed chemistry program, includ- ing G. van Iterson's courses in genetics anct plant anatomy ant! chemistry ant} M. W. Beijerinck's courses in general ant! applied microbiology. By November 1921, van Nie! had completed all the re- quirements for the chemical engineering degree except a year of work in a specialized area of his own choosing. Al- ready strongly attracted to microbiology from his exposure to Beijerinck's courses, he decided to specialize in it after hearing the inaugural lecture of A. I. Kluyver, who succeeded Beijerinck that year. Kluyver suggested that van Nie] investigate the longevity of yeast in a medium containing sugar but little or no nitro- gen. This problem provided some experience with microbi- ological and analytical methods and met the requirements for the degree, though the results were unimpressive. As a sidle project, van Nie! checked a published report that a nonmotile Sarcina conic! develop flagella and motility by repeated transfer in a special medium. His first publication (van Nie] 1923) showed that the previous author had con- fused Brownian movement with true motility and that his so- callecl flagella were artifacts of the staining method. DELFT: WORKING WITH KLUYVER After receiving his Chem. E. degree van Niel accepted a position as assistant to Kluyver. His duties consisted! of caring for a large, pure culture collection of bacteria, yeasts and fungi; assisting undergraduates; and preparing demonstra- tions for Kluyver's two lecture courses. One of the courses dealt with the microbiology of water ant! sewage in which

CORNELIS BERNARDUS VAN NIEL 393 iron ant! sulfur bacteria play a role. Since Kluyver was un- familiar with these organisms, he assigned van Nie! the task of learning to culture them so that he could provide material for class demonstrations. To fulfill this assignment, van Nie! read the publications of Winogradsky, Engelmann, Molisch, and Bavenclamm on the colorless and purple sulfur bacteria and concluded that fundamental disagreements concerning the metabolism of these organisms neecled clarification. Finding the purple bacteria "aesthetically pleasing," he con- tinuec! studying them after the lecture demonstrations were completed. During the next two years, while continuing as Kluyver's assistant, and later as conservator of the Institute, van Nie! clemonstrated that purple sulfur bacteria could grow in glass- stopperec! bottles completely filled with a mineral medium containing sulfide and bicarbonate that were exposed to day- light. (No growth occurred in the dark.) He also isolated pure cultures of a Chromatium species and Thiosarcina rosea ant! shower! that the yield of cells was proportional to the amount of sulfide provided and much greater than that of colorless aerobic sulfur bacteria in a similar medium. These observations and the earlier demonstration that O2 is not proclucect by purple bacteria were interpreted (in ac- corciance with Kluyver's theory that most metabolic reactions are transfers of hydrogen between donor and acceptor mol- ecules) to mean that purple sulfur bacteria carry out a novel type of photosynthesis in which carbon dioxide is reclucec! by hydrogen derived from hydrogen sulfide with the air! of en- ergy from light. Mentioner! briefly in Kluyver and Donker's treatise, "The Unity in Biochemistry,"i without supporting evidences this interpretation was probably based on van Niel's ' A. J. Kluyver and H. J. L Donker, "Die Einheit in der Biochemie," Chemie der Zelle und Gewebe, 13(1926): 134-90.

394 BIOGRAPHICAL MEMOIRS work. Kluyver was not a coauthor of any of van Niel's early papers on photosynthetic bacteria. During this period Kluyver and van Nie! published two papers: one clearing with a new type of yeast, Sporobolomyces (thought on the basis of its mode of spore formation to be a primitive basicliomycete), and another providing an expla- nation for the unusual morphology of a spore-forming bac- terium that grew in liquid! media as a tightly twisted, multi- strancled rope. While van Nie! expected to continue his study of purple bacteria for his Ph.D. dissertation, he also developed, as a side project, an effective methoc! for isolating propionic acid bacteria from Swiss cheese. When Kluyver pointed out that a study of this group would provide a faster path to the ctoc- torate than a completion of his investigations of the sIow- growing purple bacteria, van Nie! reluctantly agreed. He spent the next two years, therefore, studying the biochemis- try ant! taxonomy of the propionic acid bacteria. These bio- chemical studies were the first to provide a quantitative pic- ture of the products derived from the fermentations of lactate, glycerol, glucose, and starch. His taxonomic studies provided a sound basis for recognition of the species of Propionibacteraum. Van Niel's dissertation, written in English, was publisher! in 1928. An unexpected byproduct of the study of the propionic acid bacteria was the identification of ctiacety! as the com- pounc] responsible for the characteristic aroma of high qual- ity butter. Van Nie! noticed that cultures of one of his pro- pionic acid bacteria grown on a glucose medium smeller! like butter, then correlates} this oclor with the distinctive ability of the organism to produce acety~methy~carbinol, an odorless compound that is reaclily oxidizer! to diacety1, the actual source of the aroma. Van Nie} spent almost seven years in the Delft laboratory,

CORNELIS BERNARDUS VAN NIEL 395 a stimulating period cluring which Kluyver was developing his ideas about the importance of hydrogen-transfer reac- tions in metabolism and the similarity of basic biochemical reactions in clifferent organisms (the "unity in biochemistry" theory). Van Nie] consiclerec! these ideas to be among the most fundamental ant} fruitful of that era. Revering Kluyver (whom he always referrer! to as "the Master"), as one of the great scientists of the age, he was yet able at a later time to point out some of Kluyver's errors in the analysis of specific phenomena and his occasional excessive reliance on gener- alizations lacking adequate experimental support (1959,1~. PACIFIC GROVE: HOPKINS MARINE STATION In late 1927, L. G. M. Baas-Becking of Stanford Univer- sity came to Delft looking for a microbiologist to fill a position at the new Jacques Loeb Laboratory at the Hopkins Marine Station on the Monterey Peninsula. Greatly impressed by van Niel's research accomplishments and his capacity for lucid communication, he offered him an appointment as associate professor. Put off by the reputed materialism of American society, van Nie! was yet attracted by Becking's enthusiasm for the new laboratory and encouraged by Kluyver de- ciclec! to strike out on his own. He arriver! in California at the ens] of December ~ 928 and was immediately impressed by the charm of Carmel, the beautiful site of the Jacques Loeb Laboratory, and the free- dom from outside pressures that the Marine Station pro- vided. In later years he could never be persua(lec! to leave even to succeed Kluyver at the Delft laboratory. PHOTOSYNTHESIS STUDIES At the Hopkins Marine Station van Nie] continued his studies of purple and green bacteria with emphasis on the quantitative relations among substrates consumed and procl-

396 BIOGRAPHICAL MEMOIRS ucts formed. Progress was accelerates! by the finding that the bacteria grew more rapidly under continuous artificial illu- mination. He clemonstratec! that the green bacteria oxidized hydrogen sulfide only as far as sulfur, whereas the purple sulfur bacteria further oxiclized the sulfur to sulfate. Both coupled these oxidations with an essentially stoichiometric conversion of carbon dioxide to cellular materials in light- clependent reactions. The nonsulfur bacteria (Athiorhoda- ceace, which Molisch hac! grown aerobically on various or- ganic compounds) were shown to develop anaerobically, but only in the presence of carbon dioxicle and light. These ant! other observations led van Nie! to conclude that photosyn- thesis is essentially a light-dependent reaction in which hy- drogen from a suitable oxidizable compound! reduces carbon dioxide to cellular materials having the approximate com- position of carbohydrate. This was expressed by the gener- alized equation: THEA + CO2 g > 2A + (CH2O) + H2O. According to this formulation, H2O is the hydrogen donor in green plant photosynthesis and is oxi(lizecl to O2, whereas H2S or another oxidizable sulfur compound is the hydrogen donor for purple and green sulfur bacteria, and the oxida- tion product is sulfur or sulfate, depencling on the organism. The nonsulfur purple bacteria that require suitable organic compounds in addition to carbon clioxide for anaerobic growth in light were presumed to use these compounds as hydrogen donors ant! to oxidize them either partially or completely. Later, the purple sulfur bacteria were also shown to use some organic compounds in place of H2S in their pho- tometabolism. These observations ant! interpretations, the results of some six years of investigation, were first presented at a small meeting of the Western Society of Naturalists in Pacific Grove

CORNELIS BERNARDUS VAN NIEL 397 at the end of 1929. Two years later van Nie! published a de- tailecl account of the culture, morphology and physiology of purple and green suIphur bacteria (193l,1), bringing his in- terpretation of their metabolism and its implications for green-plant photosynthesis to the attention of a wider aucli- ence. All of the purple sulfur bacteria he isolated were relatively small organisms, belonging to what he called Chromatium, Thiocystis, and Pseudomonas types. In material collected in nature (and in some enrichment cultures) he observed a number of larger forms but, despite numerous attempts, was unsuccessful in isolating them. The cultivation of these or- ganisms was not accomplished until many years later, when N. Pfennig and H. G. SchIegel, both onetime associates of van Niel, discovered that nutritional and environmental re- quirements are more complex than had been previously rec- ognizecl.2 Van Nie} published a large monograph covering many years of work on the culture, general physiology, morphology and classification of the nonsulfur purple and brown bacteria in 1944 (1944,21. He classified over 150 strains isolated from natural sources into six species in two genera Rhodospeudo- monas and RhodospiraZlum. He clescribec! the morphology of the organisms, their pigments, nutritional requirements, and metabolism in the presence and absence of light. As in all his publications, van Nie] also reviewed the historical back- grounc! and current literature of the subject critically and thoroughly. Following the recognition of several types of photosyn- thesis using different hydrogen donors, van Nie! began to 2 H. G. Schlegel and N. Pfennig, "Die Anreicherungskultur einiger Schwefelpur- purbakterien." Archiv fur Mibrobiologie, 38(1961): 1-39, and N. Pfennig and K. D. Lippert, "Uber das Vitamin Be Bedurfnisphototropher Schwefelbakterien." Archiv fur Mibrobiologie, 55(1966):245-56.

398 BIOGRAPHICAL MEMOIRS consider how radiant energy participates in these reactions. There appeared! to be two possibilities, both consiclered by earlier investigators: radiant energy could be used to activate either carbon dioxicle or the hydrogen donor. Initially, van Nie} and Muller (1931,2) were incliner! to believe that light is used primarily to activate carbon dioxide, a relatively stable compound and the common reactant in all photosynthetic systems. But they die! not exclude the seconc! possibility, that light also activated the hydrogen donor. In this connection they notes! a correlation between the pres- ence of nonchIorophyI] yellow ant! red pigments ant! the na- ture of the hydrogen (loner used by different organisms. These pigments, lacking in the green sulfur bacteria that uti- lize the easily oxiclizable hydrogen sulfide, occur exclusively . . . - ~n organisms up Zing water or sulfur, then thought to re- quire a greater activation. This led van Nie! to undertake a series of studies of the pigments of the purple and green bacteria. Van Nie} and Arnold (193S,1) developed a convenient spectrophotometric method for determining the amount of bacteriochIorophyI] in photosynthetic purple and brown bac- teria uncler conditions avoiding interference by the rec! car- otinoi(1 pigments. They also reported that van Nie! and E. Wieclemann, working in A. Stoll's laboratory, had examined the green pigments of six clifferent strains of purple and brown bacteria ant! concluded that they were identical with the chlorophyll of the purple sulfur bacterium, Thiocystis, previously stucliect by H. Fischer. Van Nie] and Smith (1935,2) began a study of the chem- istry of the major red pigment of the nonsulfur purple bac- terium, Rhodospirillum rubrum. By solvent extraction and re- peated crystallization, they isolated about 100 milligrams of an apparently homogeneous carotinoid they called "spirillo- xanthin." Its empirical composition was found to be

CORNELIS BERNARDUS VAN NIEL 399 C48H66O3, and it contained fifteen double bonds, no more than one hydroxyl group, and no free carboxyl group—mak- ing it the most highly unsaturated carotinoid then known. Rhodoviolascin, a red pigment that had almost the same absorption spectrum and melting point as spirilloxanthin, was later isolated by Karrer and Solmssen from a nonsulfur purple bacterium identified as Rhodovibrio.3 This compound contained two methoxy] groups and had the empirical for- mula C40H54~0CH312. Polgar, van Niel, and Zechmeister (1944,1) redetermined the molecular weight and composi- tion of spirilloxanthin using material purified by column chromatography and concluded that the formula established by Karrer and Solmssen was correct and that rhodoviolascin and spirilloxanthin are identical. They also found that spi- rilloxanthin is unstable and reversibly converts, under rela- tively mild conditions, to two compounds designated neo- spirilloxanthin A and B. which can be separated from spirilloxanthin chromatographically. A study of the absorp- tion spectra of these compounds under various conditions led to the conclusion that spirilloxanthin is an all-trans com- pound, whereas neospirilloxanthin-A probably contains two cas double bonds, one of which is centrally located. In a broader review of the known properties of red pigments derived from various nonsulfur purple bacteria, van Nie! (1944,2) concluded that, in addition to spirilloxanthin, at least two other pigments occur in these organisms, distin- guishable by their melting points and absorption spectra. When anaerobic cultures are exposed to oxygen, some strains of nonsulfur purple bacteria undergo a dramatic color change from yellow-brown to deep red. Van Nie} (1947,1) investigated this phenomenon in L. Zechmeister's 3 P. Karrer and U. Solmssen,"Die Carotinoide der Purpurbakterien I," Helvetica Chimica Acta 18(1935):1306-15. Parts II and III of this article appear in Helvetica Chimica Acta 19(1936):3 and 1019.

400 BIOGRAPHICAL MEMOIRS laboratory. Using cells of Rhodopseualomonas spheroides grown uncier semianaerobic conditions in continuous light, he iso- lated the two most abundant red and yellow carotinoid pig- ments as crystalline products. Both pigments were shown to have all-trans configurations and, as previously shown for spi- rilloxanthin, were easily converted to the c~s-isomers. In or- der to follow the pigment changes associated with exposure of anaerobically-grown cells to oxygen, a spectrophotometric methoc} was developed to determine the amounts of rec! and yellow pigments in a mixture obtained by extracting a cell suspension. Using this method the yellow pigment was shown to be partially and irreversibly converted to the red pigment when anaerobically-grown cells were exposer} to oxygen. As previously notes! by C. S. French, the conversion of the yellow carotinoic! to red occurred! only in the presence of actively metabolizing bacteria. The nature of the chemical transfor- mation responsible for the color change was not determined. Studies in several laboratories of the role of various pig- ments in photosynthesis and phototaxis by Rhoa~ospirillum rub- rum had resulted in conflicting conclusions as to whether spi- rilloxanthin with absorption maxima at 550,510 and 480 nm, or another pigment with maxima at 530,490 and 460 nm was the photoactive compouncl. A possible explanation for this discrepancy was provided by L. N. M. Duysen,4 who ob- serve(1 that the absorption spectrum, and therefore presum- ably the pigment composition, of R. rubrum changed with the age of the culture. Young cultures showed a minor 530 nm absorbance peak, gradually replaced by the 550 nm peak of spirilloxanthin as the culture aged. This observation was con- firmect by van Nie! and Airth (unpublished work, 1954) with two strains of R. rubrum. Van Niel, Goodwin, and Sissins 4 lo. N. M. Duysens, unpublished doctoral thesis for the University of Utrecht, 1952.

CORNEElS BERNARDUS VAN NIEE 401 ~1956, ~ ~ subsequently identified the carotinoids in young cul- tures and showed that these indeed decreased with time, while spirilloxanthin increased from about twenty percent of the total carotinoids in a one-day-old culture to about ninety percent in a five-day culture. These studies provided information concerning the iden- tity and properties of the pigments of photosynthetic bacteria but did little to clarify the role of the pigments in photosyn- thesis. By 1936 van Niel's interpretation of the role of the pho- tochemical system . in photosynthesis had changed radically (1936,31. He had abandoned the earlier theory that radiant energy participated directly in carbon dioxide activation when he recognized that various nonphotosynthetic bacteria, including several chemoautotrophic species, methanogenic bacteria and propionic acid bacteria, readily utilized carbon dioxide in the dark. Furthermore, the idea that each of the many inorganic and organic compounds used as substrates by the photosynthetic bacteria were directly involved in a photochemical reaction appeared unlikely, particularly since van Nie} had shown that certain organic compounds used by the nonsulfur purple bacteria are oxidized both in the dark with O2 or in the light in the absence of O2. He later dem- onstrated that even the rates of organic substrate oxidation are the same in the dark and in the photosynthetic reaction, provided the light intensity is sufficiently high (1941,2; 1949,2~. Van Nie! finally concluded that both plant and bacterial photosynthetic reactions have a common photochemical re- action: the photolysis of water to form a strong reducing agent and a strong oxidizing agent. He postulated that the reducing agent was used, through a series of enzymatic re- actions, to convert carbon dioxide to cellular constituents; whereas the oxidizing agent was used either to generate O2

402 BIOGRAPHICAL MEMOIRS in green plant photosynthesis or to oxidize the hydrogen clo- nor in bacterial photosynthesis. Van Niel's unified interpre- tation of the photochemical event in photosynthesis is similar in principle to the current interpretation of this process, al- though a special type of chlorophyll (rather than water) is now considered to be the source of the light-generatec} oxi- dizing and reducing species. In collaboration with H. Larsen ant! C. S. Yocum, van Nie! investigated the energetics of photosynthesis in green sulfur bacteria supplier! with different reducing agents with the ob- ject of determining whether the energy released by oxidation of the reducing agents was uses] to reduce carbon dioxide (1952,31. They determined the number of light quanta used to convert one molecule of CO2 into cell material when either H2, thiosulfate, or tetrathionate was used as the reducing agent. Photosynthesis with H2 was expected to require about 2S,000 calories less than with the other substrates because of the large energy change associated with H2 oxidation, but- finding that the number of light quanta required to reduce one molecule of CO2 was approximately the same with all three substrates they concluclec! that the energy obtained by the oxidation of the electron donor is not used for CO2 · .. . asslmllatlon. Several other postdoctoral fellows who studied with van Nie] made significant contributions to understanding the biology and physiology of photosynthetic bacteria. Providing background and inspiration for these investigations, van Nie! gave encouragement and advice during the experimental work, evaluatecl results critically, and aided in preparing the manuscripts but was seldom willing to become a coauthor of the final publications. Many of his own scientific contri- butions, consequently, are embedclecl in the publications of his associates, as in F. M. Muller's 1933 publications on the utilization of organic compounds by purple sulfur bacteria;

CORNELIS BERNARDUS VAN NIEL 403 i. W. Foster's 1944 paper on the coupling of CO2 reduction to the officiation of isopropano! to acetone by nonsulfur purple bacteria; H. Larsen's works in 1952 and 1953 on the culture and physiology of green sulfur bacteria; and R. K. CIayton's 1955 report on the relation between photosynthesis and respiration in Rhodospirillum rubrum. Van Niel's influence can also be seen in Pfennig's work on the nutrition and ecol- ogy of photosynthetic bacteria. METHANE PRODUCTION AND CARBON DIOXIDE UTILIZATION Van Niel's studies of photosynthetic bacteria led him to consider other processes in which carbon dioxide utilization might occur. In the early 1930s he had postulated that meth- ane formation from organic compounds by anaerobic bac- teria was the result of carbon ctioxide reduction. This idea was based upon the investigations of N. L. Sohngen, a stu- dent of Beijerinck who tract studier! the decomposition of lower fatty acids by methanogenic enrichment cultures under anaerobic conditions and found that formate and lower fatty acids with an even number of carbon atoms are converted quantitatively to carbon dioxide and methane. The identity of the products, therefore, was independent of the chain- length of the substrate. Sohngen's cultures, furthermore, could convert hydrogen and carbon dioxide to methane ac- corcling to the equation: 4H2 + CO2 ~ CH4 + 2H2O. Since carbon dioxide is clearly reduced to methane in this reaction, van Nie! concluded that this also occurs in the fer- mentation of fatty acicis. Carbon cTioxicle, in other words, was postulates! to serve as hydrogen acceptor for the oxidation of fatty acids to carbon ctioxi(le and water. This coul(1 explain why methane is the only reduced compound formed in the

404 BIOGRAPHICAL MEMOIRS methane fermentation of organic compounds—a theory that received support from the 1939-1940 demonstration by H. A. Barker that a purified culture of a methanogen appar- ently coupled the oxidation of ethanol to acetic acid with the reduction of carbon dioxide to methane. In 1967, however, M. P. Bryant et al. found that the culture contained two kinds of bacteria one which oxidizes ethanol to acetate ant! H2, and the methanogen that converts H2 and carbon dioxide to methane. The formation of methane from all but a few organic compounds now appears to require a similar participation of a non-methanogenic bacterium. Van Niel's carbon dioxide reduction theory of methane formation from organic com- pounds, consequently, is valid only for the syntrophic asso- aatlon ot two spears. Following the early studies of S. Ruben ant! M. D. Kamen at the University of California, Berkeley, on biological carbon dioxide fixation by use of the short-livec! carbon isotopes ~ ~C, van Nie} and some of his students collaborated in similar studies with propionic acid bacteria,5 fungi,6 and protozoa (1942,31. The experimenters sought to confirm and extend the unexpected discovery of H. G. Wood and C. H. Werkman that succinic acid is former! in part from carbon dioxide. The ciliate Tetrabymena geleii was also shown to incorporate carbon dioxicle into succinate, whereas the fungi Rhizopus nigricans and Asperg~lus niger incorporates! carbon dioxide into the carboxy! groups of fumarate and citrate, respectively. Van Niel's special contribution to these investigations was his attempt to unclerstand the general requirement of non- 5 S. F. Carson, J. W. Foster, S. Ruben, and H.A. Barker, "Radioactive carbon as an indicator of carbon dioxide utilization. V. Studies on the propionic acid bacteria." PNAS 27(1941):229 - 35. 63. W. Foster, S. F. Carson, S. Ruben, and M. D. Kamen, "Radioactive carbon as an indicator of carbon dioxide utilization. VII. The assimilation of carbon dioxide by molds. PNAS 27(1941):590-96.

CORNELIS BERNARDUS VAN NIEL 405 photosynthetic microorganisms for carbon dioxide ant! the mechanism of its fixation (1942,2~. He concluclec} that carbon dioxicle fixation generally occurs by carboxylation reactions and that carbon dioxide is probably required to counteract the clecarboxylation of oxaloacetate, which "constitutes a 'leak' through which certain essential cell constituents are ctrainec} off." In 1935 H. A. Barker, at van Niel's suggestion, undertook a stucly of the respiratory activity of the colorless algae Pro- totheca zoppi. His original objective was to use Otto Warburg's manometric method to identify the organic compounds that the organism couIct oxidize and to determine the quantities of O2 consumer! ant] CO2 proclucec! from a known quantity of each substrate. The ciata showed that the amounts of O2 and CO2 were far below those required for complete oxida- tion, the gas exchange accounting for only seventeen to fifty percent of that required for complete oxidation depending on the particular substrate. The rest of the substrate was ap- parently converter! into storage or cellular materials with the approximate empirical composition of carbohydrate. This unexpectedly high conversion of respiratory substrates to cell materials became known as oxiciative assimilation. In Kluyver's laboratory, G. Giesberger and C. E. Clifton subse- quently obtained similar results with several bacteria. Because of its apparent relation to the synthesis of cell materials in photosynthesis and the general problem of the utilization of the products and energy of respiration for as- similatory purposes, van Nie] maintained a continuing inter- est in this phenomenon. He ancl his students studied assim- ilation reactions of both yeast and bacteria, the most interesting result being the demonstration that yeast but not lactic acid bacteria assimilate about thirty percent of the glu- cose clecomposec! uncler anaerobic conditions a process they called "fermentative assimilation."

406 Bacterial Taxonomy BIOGRAPHICAL MEMOIRS One of van Niel's most enduring scientific interests out- side of photosynthesis and photosynthetic bacteria was bac- terial taxonomy. In his cloctoral dissertation he tract reviewed what he called "the main features of bacterial taxonomy" and proposer! a possible sequence for the evolution of various morphological types of bacteria. Starting from a presumably primitive, nonmotile, spherical cell, it progressed along three postulated evolutionary lines to polarly flagelIatecI spirilIa, peritrichously flagellate sporulating rods, and permanently immotile rocis forming conictia. With small mollifications, this concept of morphological evolution former! the basis of the taxonomic system proposed by Kluyver and van Nie} (1936,41. Four morphological fam- ilies cleaned by cell shape, type of flagellation, and sporula- tion were subdiviclec! by morphology into eleven tribes. The organisms in the morphological tribes were further assigned to sixty-three genera on the basis of types of energy metab- olism, substrate utilization and among chemo-hetero- trophic anaerobes- products of metabolism. Although rec- ognizing that this taxonomic system was an over- simplification, the authors believed that it was more rational ant! "natural," i. e., phylogenetic, than previous systems. In 1941, van Nie! and R. Y. Stanier undertook an analysis of the problems of classification of the larger taxonomic units among microorganisms (1941,31. After pointing out glaring deficiencies in the definitions of major microbial groups in Bergey's Manual,7 they concluder! that for larger taxa, mor- phological characteristics should be given priority over phys- iological characteristics. On this basis they clecicled that the blue-green algae (Myxophyta) and the bacteria (Schizomy- 7 Bergey's Manual of Determinative Bacteriology, ed. D. H. Bergey, Baltimore: Williams and Wilkins Co., 5th edition, 1936.

CORNELIS BERNARDUS VAN NIEE 407 cetae) shouIcl be combined in the kingdom, Monera, which comprises organisms without true nuclei, plastics, and sexual reproduction. The Schizomycetae were then separated into four classes: Eubacteriae, Myxobacteriae, Spirochaetae, anc! a heterogeneous group of organisms not falling into the other classes. The Eubacteriae were further separated into three orders (Rhoclobacteriales, Eubacteriales, Actinomyce- tales) on the basis either of type of metabolism (photosyn- thetic, nonphotosynthetic) or cell organization (unicellular, mycelial). Each of these groups was defined as precisely as possible with the information available, the authors empha- sizing that the proposed system was a first ciraft and subject to revision as new information accumulated. By 1946, van Nie! no longer believed that a taxonomic system baser! on phylogenetic considerations was possible in view of the relatively few morphological properties of bac- teria, the general absence of developmental processes, and the probability of the occurrence of both convergent and di- vergent evolution in the development of existing groups (1946, Id. He pointed out that attempts to classify bacteria in a single system by the use of morphological, physiological, nutritional, and ecological properties was only partially suc- cessful. Since different properties often overlapped, a single organism conic! be assigned to more than one taxonomic group or could not be readily assigned to any. He concluded that attempts to accommodate all known bacteria in a single taxonomic system should be abandoned until more infor- mation on phylogenetic relationships was available. He went so far as to suggest that the use of binomial nomenclature should be cliscontinueci until phylogenetic relationships could be firmly establisher! ant! proposed, in the meantime, bacteria could be iclentified more readily by multiple keys based upon any of several conspicuous and reaclily cletermin- able properties. By 1955, van Nie! had become skeptical of the possibility

408 BIOGRAPHICAL MEMOIRS of separating bacteria ant! blue-green algae from other or- ganisms on the basis that they lacked nuclei, plastics, and sexual reproduction. New developments had weakened or destroyed these negative criteria as ctifferential characters. He noted that some bacteria contained "discrete structures that might be considered, on the basis of their behavior and chemical nature, as nuclei"; that photosynthetic pigments of some purple bacteria ant} blue-green algae were located in uniform spherical particles rather than being distribute{] evenly throughout the cells; and that, in E. coli, an exchange of genetic characters between cells had been clearly demon- strated ~ ~ 955, ~ ). On the basis of new information developed since van Niel's 1955 paper, Stanier and van Nie! (1962,2) again ex- aminect the criteria user! to distinguish bacteria and blue- green algae from viruses ant! other protists. In agreement with Two, they notes! that the structures and mocles of reproduction of viruses chider from those of bacteria and that no ambiguity existed as to the taxonomic position of rickett- sia, pleuro-pneumonia-like organisms, and other obligately parasitic bacteria. The bacteria and blue-green algae were separated from all other protists by the procaryotic nature of their cells. They distinguished the procaryotic from the eu- caryotic cell by the absence of internal membranes separating nuclear material and when present—respiratory and pho- tosynthetic apparatuses from each other and from the cyto- plasm. In acictition, the nuclei of procaryotes divide by fission rather than by mitosis, their cell walls contain mucopepticles as a strengthening element, and the structure of the flagella, when present, is unique. The authors concluder! that there was no adequate basis for separating bacteria from blue- green algae. 53. ~ A. L.woff, "The concept of virus." journal of General Microbiology, 17(1957):239-

CORNELIS BERNARDUS VAN NIEL 409 DENITRIFICATION Van Niel published two papers dealing with aspects of the chemistry of denitrification. Allen and van Nie} (1952,1) in- vestigated the pathway of nitrite reduction by Pseudomonas stutters. Initially they tested the possibility that the conversion of nitrite to N2 may involve a reaction between nitrite and an amine, but no supporting evidence could be obtained. They then tested possible intermediates in nitrite reduction by the technique of simultaneous adaptation and the use of various inhibitors and found that neither N2O nor hyponitrite could fulfill this role. Nitramide, H2N. NO2, however, was found to be reduced readily to N2 at about the same rate as nitrite and the utilization of both compounds was inhibited by cyanide to the same extent. Nitramide, consequently, was considered to be a possible intermediate in denitrification. In 1920 Warburg and Negelein reported that algae ex- posed to light in a nitrate solution produce O2 in the absence of added carbon dioxide. They postulated that the algae used nitrate to oxidize cellular organic compounds to carbon diox- ide, which was then used for O2 production by photosyn- thesis.9 Van Niel, Allen, and Wright proposed the alternative in- terpretation that nitrate replaces carbon dioxide as the elec- tron acceptor in photosynthesis (1953,11. They showed that when nitrate-adapted Chlorella is exposed to high light- intensity in a medium containing excess carbon dioxide, the rate of O2 production increased with the addition of nitrate. This increased rate could not have been caused by an increase in carbon dioxide production, since the reaction was already saturated with this compound. The higher rate, then, could 9 O. Warburg and E. Negelein, "Uber die Reduktion der Saltpetersaure in grunen Zellen." Biochemische Zeitschnit, 1 10(1920):66-1 15.

410 BIOGRAPHICAL MEMOIRS only result from the utilization of nitrate as an additional electron acceptor. VAN NIEL THE GENERALIST As his reputation as a scientist and teacher spread, van Nie! responded to many invitations to lecture ant} write re- views. In the early part of his career these mostly dealt with bacterial photosynthesis and its relation to plant photosyn- thesis. Later he often clealt with broader topics such as "The Delft School and the Rise of General Microbiology" (1949,4), "The Microbe as a Whole" ~ ~ 955,4), "Natural Selection in the Microbial WorIcI" (1955,3), "Evolution as Viewed by the Mi- crobiologist" ~ ~ 956,2c), and "Microbiology and Molecular Biology" (1966,1~. He always displayed an impressive com- mand of historical background; and current literature and a notably clear, analytical, and elegant style of presentation. "On radicalism and conservatism in science" (1955,2), his presidential adciress to the Society of American Bacteriolo- gists in 1954, was a clear statement of van Niel's personal philosophy a strong preference for the heretical and un- conventional over established and accepted clogma, despite his recognition of the weaknesses and strengths of both. For him the essence of science was the clevelopment of an attitude of mind that "accepts experience as the guiding principle by which it is possible to test the relative merits of opposing viewpoints by means of carefully conducted, controlled ex- periments," and "recognizes equally keenly that our knowI- edge and capacities are exceedingly limited, not merely if consi(lerect from the standpoint of the inclivi(lual, but even with reference to the combiner! experience of the human race." He concluclecl that the most clesirable mental charac- teristics of a scientist are objectivity and tolerance, and that his greatest satisfaction should derive from "having enriched the experience of his fellow men."

CORNELIS BERNARDUS VAN NIEL 411 Van Niel's chapter on "Evolution as Viewed by the Micro- biologist" (1956,2c) proviclecl a stimulating synthesis of ideas concerning the origin of life and the relation of living to nonliving systems. By the application of both logic and in- tuition to the available scientific information and theory, he developed the hypothesis that life is a special property of matter that inevitably appears when chemical systems reach a state of sufficient complexity under suitable conditions. His generalized concept of evolution comprised physical, chem- ical, biochemical, ant! biological phases of which only the last corresponds with evolution in the Darwinian sense. TEACHER AND COLLEAGUE In addition to being an outstanding investigator, van Nie! was a superlative teacher, and his greatest contribution to science may well have been his teaching of general microbi- ology and comparative biochemistry. Soon after coming to the Hopkins Marine Station he be- gan offering a ten-week laboratory course in microbiology. Initially, the content of the course was similar to that given at Delft and consisted! of an introduction to methods of isolating and identifying microorganisms in commercial yeast, milk, water, and soil. But van Nie! soon realized that neither Beijerinck's elective culture methods baser! on the principle of natural selection—nor Kluyver's ideas about comparative biochemistry were appreciated in this country. He therefore undertook to develop a course emphasizing these approaches to microbiology and biochemistry. Van Niel's students learned how numerous morphological and physiological types of bacteria, when their nutritional and environmental requirements were known, conic! be enriched and isolated from natural sources. He discussed the metabolism of each group, emphasizing the most recent fin(lings regarding in- termediary metabolism, similarities and differences in deg- .

412 BIOGRAPHICAL MEMOIRS radative pathways, and the chemical and energetic relations between degraciative metabolism and the synthesis of cellular components. He examiner! the structure of bacterial cells, aspects of bacterial genetics, variation and adaptation, bac- terial and yeast taxonomy, and the philosophy of science. The course was organized as a series of relatively simple experiments for which van Nie! provider! the background, rationale, and interpretation of results. He was always in the laboratory guiding the work and commenting on each stu- dent's observations and results ant! often used the Socratic method, stimulating students to make judgments about the meaning of their observations ant! sometimes intentionally leading them to some plausible but incorrect conclusion so that a later experiment, already plannecI, would reveal the error. After a topic or phenomenon hac! been introcluced in a laboratory experiment, he would launch into a presentation of its historical background, usually starting with the most primitive ideas and progressing to the latest developments. He always placed great emphasis on possible alternative in- terpretations of the available information at each phase of scientific development and on the frequently slow and difii- cult process of moving from clearly erroneous to more nearly correct but neverimmutable conclusions. His lectures often lasted for several hours and were pre- sented with such clarity and histrionic skill as to capture the complete attention and stimulate the enthusiasm of his stu- clents. As the course developer! over the years along with the literature of microbiology, lectures took up a larger propor- tion of the available time. The course expanded from three afternoons to three days a week, with class hours often ex- tending from eight in the morning to well into the evening, with time out only for lunch ant! tea and coffee breaks. The course was very strenuous for van Niel, who was never par- ticularly robust, and in his later years he was so exhausted by its end he needed some weeks to recuperate. . .

CORNELIS BERNARDUS VAN NIEL 413 During the early years, only a few students attended, but as van Niel's reputation as a teacher spread, the class hack to be limited, initially to eight, and later to fourteen students- the number that conic! be accommociated in the small Marine Station laboratory. The students were initially undergraduate or graduate students from Stanford, but later a large pro- portion came from other institutions. In 1950, for example, only one of the thirteen students was from Stanford. The others were from Washington University, Wisconsin, Michi- gan, Missouri, California Institute of Technology, Connecti- cut, Illinois, Cambridge, and the University of California at Los Angeles. In addition there were eleven auditors of the discussions and lectures who clid not do the experiments- mostly postdoctoral fellows or established scientists who wished to extend their background in general microbiology. The lists of students and auditors who attended van Niel's course between 1938 and 1962 reads like a Who's Who of bio- logical scientists in the United States, with several, as well, from other countries. Both clirectly, and indirectly through his students, van Nie! exerted a powerful influence on teach- ing and research in general microbiology for a generation. Although his own research was concerned mainly with photosynthetic bacteria, van Nie! was interested in the biol- ogy and metabolism of many other groups of microorga- nisms. He clicl not believe in directing the research of his younger associates but rather encouraged them to follow their own interests, some of which hac! been stimulated by his lectures and personal discussions. As a consequence, the range of phenomena investigated in his laboratory was ex- ceedingly wide and included the culture and physiology of blue-green algae and diatoms, nutritional and taxonomic studies of plant-pathogenic bacteria, biological methane for- mation, pteridine and carbohydrate metabolism of protozoa, germination of mold spores, biology of caulobacteria, culti- vation of free-living spirochetes, induction of fruiting bodies

414 BIOGRAPHICAL MEMOIRS in myxobacteria, decomposition of cellulose, the role of mi- croorganisms in the foot! cycle of aquatic environments, ad- aptation of bacteria to high salt concentrations, cultivation of spirilIa anct colorless sulfur bacteria, bacterial fermentations, thermophylic bacteria, denitrification, pyrimidine metabo- lism, and the thermodynamics of living systems. To all stu- dents van Nie} gave freely of his time, advice and enthusiasm, drawing on his own extraordinary knowledge of the litera- ture. RETIREMENT Following his retirement from the Marine Station in 1962, van Nie! held a visiting professorship at the University of California at Santa Cruz from 1964 to 1968, teaching part of a freshman-level biology course in collaboration with K. V. Thimann ant! L. Blinks. After 1972, van Nie! gave up teaching and research en- tirely and clisposec! of his scientific library ant! large collection of reprints. Thereafter he lived quietly with his wife, Mimi, in Carme! ant! spent his leisure reading classical and modern literature and listening to classical music, which he greatly enjoyed. He was often visited by former students who con- tinued to be impressed by the warm hospitality of his home, the charm of his personality, the breadth of his understancl- ing, ant! the comprehensiveness of his memory.

CORNELIS BERNARDUS VAN NIEL 415 HONORS AND DISTINCTIONS DEGREES AND HONORARY DEGREES 1923 Chemical Engineering, Technical University, Delft 1928 D.Sci., Technical University, Delft 1946 D.Sci. (Honorary), Princeton University 1954 D.Sci. (Honorary), Rutgers University 1968 LL.D., University of California, Davis FELLOWSHIPS AND PROFESSIONAL APPOINTMENTS 1925-1928 Conservator, Laboratorium voor Microbiologie, Delft 1928-1935 Associate Professor of Microbiology, Stanford Uni- versity, Hopkins Marine Station 1935 -1936 Rockefeller Foundation Fellow 1935-1946 Professor of Microbiology, Stanford University 1945 John Simon Guggenheim Fellow 1946-1963 Herstein Professor of Biology, Stanford University 1955-1956 John Simon Guggenheim Fellow 1963-1985 Herstein Professor, Emeritus, Stanford University 1964-1968 Visiting Professor, University of California, Santa Cruz AWARDS AND HONORS 1942 Stephen Hales Prize, American Society of Plant Physiology 1964 Emil Christian Hansen Medalist, Carlsberg Foundation of Copenhagen 1964 National Medal of Science 1966 Charles F. Kettering Award, American Society of Plant Physiology 1967 Rumford Medal, American Society of Arts and Sciences 1967 Honorary Volume, Archiv fur Mikrobiologie 1970 Antonie van Leeuwenhoek Medal, Royal Netherlands Academy of Sciences LEARNED SOCIETIES 1945 National Academy of Sciences 1948 American Philosophical Society 1950 American Academy of Arts and Sciences 1952 Charles Reid Barnes Life Membership, American Society of Plant Physiology

416 BIOGRAPHICAL MEMOIRS 1954 President, American Society for Microbiology 1954 Corresponding Member, Academy of Sciences, Gottingen, Germany 1958 American Academy of Microbiology 1963 Honorary Member, Societe Franchise de Microbiologie 1967 Honorary Member, Society of General Microbiology 1968 Honorary Member, Royal Danish Academy of Sciences and Letters

CORNELIS BERNARDUS VAN NIEL 417 SELECTED BIBLIOGRAPHY 1923 Uber die Beweglichkeit und das Vorkommen von Geisseln bei einigen Sarcina Arten. Zentralbl. Bakteriol. Parasietenkd. In- fektionskr. Hyg., Abt. II., 60:289-98. 1924 With A. J. Kluyver. Uber Spiegelbilder erzeugende Hefearten und die neue Hefegattung Sporobolomyces. Zentralbl. Bakteriol. Par- asitenkd. Infektionskr. Hyg., Abt. II., 63:1-20. 1925 With F. Visser't Hooft. Die fehlerhafte Anwendung biologischer Agenzien in der organischen Chemie. Eine Warnung. Ber. Dtsch. Chem. Ges., 58: 1606-10. 1926 With A. }. Kluyver. Uber Bacillus funicularis n.sp. nebst einigen Be- merkungen uber Gallionella ferrug~nea Ehrenberg. Planta, 2:507-26. 1927 With A. ]. Kluyver. Sporoboloymces ein Basidiomyzet? Ann. Mycol. Notitiam Sci. Mycol. Univ., 25:389-94. Notiz uber die quantitativ Bestimmung von Diacetyl und Acetyl- methylcarbinol. Biochem. Z., 187:472-78. 1928 The Propionic Acid Bacterza. (Doctoral Dissertation.) Haarlem, The Netherlands: Uitgeverszaak]. W. Boissevain & Co. 1929 With A. J. Kluyver and H. G. Derx. De bacterien der roomverzur- ing en het boteraroma. Verslag gewone Vergader. Afd. Na- turrkd. Nederl. Akad. Wetensch., 38:61-2. With A. J. Kluyver and H. G. Derx. Uber das Butteraroma. Bio- chem. Z., 210:234-51.

418 BIOGRAPHICAL MEMOIRS 1930 Photosynthesis of bacteria. In: Contributions to Marine Biology, Stan- ford: Stanford University Press, pp. 161-69. 1931 On the morphology and physiology of the purple and green sulfur bacteria. Arch. Mikrobiol., 3:1-112. With F. M. Muller. On the purple bacteria and their significance , ~ for the study of photosynthesis. Rec. Trav. Bot. Neer., 28:245- 74. 1935 Photosynthesis of bacteria. Cold Spring Harbor Symp. Quant. Biol., 3: 138-50. With J. A. C. Smith. Studies on the pigments of the purple bacteria. I. On spirilloxanthin, a component of the pigment complex of Spirillum rubrum. Arch. Mikrobiol., 6:219-29. A note on the apparent absence of Azotobacter in soils. Arch. Mi- krobiol., 6:215 -18. 1936 On the metabolism of the Thiorhodaceae. Arch. Mikrobiol., 7:323-58. With D. Spence. Bacterial decomposition of the rubber in Hevea latex. Ind. Eng. Chem., 28:847-50. Les photosyntheses bacteriennes. Bull. Assoc. Diplomes Microbiol. Fac. Pharm. Nancy, 13:3-18. With A. J. Kluyver. Prospects for a natural system of classification of bacteria. Zentralbl. Bakteriol. Parasitenkd. Infektionskr. Hyg. Abt. II, 94:369-403. 1937 The biochemistry of bacteria. Ann. Rev. Biochem., 6:595-615. 1938 With W. Arnold. The quantitative estimation of bacteriochloro- phyll. Enzymologia, 5:244-50.

CORNELIS BERNARDUS VAN NIEL 419 1939 A. l. Kluyver. Als mikrobioloog en als biochemikus. Chem. Weekbl., 36: 1-109. 1940 The biochemistry of microorganisms: An approach to general and comparative biochemistry. Am. Assoc. Adv. Sci. Publ., 14:106- 19. 1941 With E. H. Anderson. On the occurrence of fermentative assimi- lation. I. Cell. Comp. Physiol., 17:49-56. The bacterial photosyntheses and their importance for the general problem of photosynthesis. Adv. Enzymol., 1 :263-328. With R. Y. Stanier. The main outlines of bacterial classification. I. Bacteriol., 42:437-66. 1942 With A. L. Cohen. On the metabolism of Candida albicans. ]. Cell. Comp. Physiol., 20:95-112. With S. Ruben, S. F. Carson, M. D. Kamen, and I. W. Foster. Ra- dioactive carbon as an indicator of carbon dioxide utilization. VIII. The role of carbon dioxide in cellular metabolism. Proc. Natl. Acad. Sci. USA, 28:8-15. With I. O. Thomas, S. Rubin, and M. D. Kamen. Radioactive car- bon as an indicator of carbon dioxide utilization. IX. The assim- ilation of carbon dioxide by protozoa. Proc. Natl. Acad. Sci. USA,28:157-61. 1943 Biochemistry of microorganisms. Ann. Rev. Biochem., 12:551-86. Biochemical problems of the chemo-autotrophic bacteria. Physiol. Rev., 23:338-54. 1944 With A. Polgar and L. Zechmeister. Studies on the pigments of the purple bacteria. II. A spectroscopic and stereochemical inves- tigation of Spirilloxanthin. Arch. Biochem., 5:243-64. The culture, general physiology, morphology, and classification of

420 BIOGRAPHICAL MEMOIRS the nonsulfur purple and brown bacteria. Bacteriol. Rev., 8:1- 118. Recent advances in our knowledge of the physiology of microor- ganisms. Bacteriol. Rev., 8:225-34. 1946 The classification and natural relationships of bacteria. Cold Spring Harbor Symp. Quant. Biol., 11:285-301. 1947 Studies on the pigments of the purple bacteria. III. The yellow and red pigments of Rhodopseudomonas spheroides. Antonie van Leeu- wenhoek T. Microbiol., 12: 156 - 66. 1948 Propionibacterium, pp. 372-79; Rhodobacterineae, pp. 838-74; Beggiatoaceae, pp.988-96; Achromatiaceae, pp.997-1001. In: Bergey's Manual of Determinative Bacteriology, 6th ea., eds. R. S. Breed, E. G. D. Murray, and A. P. Hitchens, Baltimore: Williams and Wilkins Co. 1949 The kinetics of growth of microorganisms. In: The Chemistry and Physiology of Growth, ed. A. K. Parpart, Princeton: Princeton University Press, pp. 91-105. The comparative biochemistry of photosynthesis. In: Photosynthesis in Plants, eds. I. Franck and W. E. Loomis, Ames: Iowa State College Press, pp. 437-95. Comparative biochemistry of photosynthesis. Am. Sci., 37:371-83. The "Delft school" and the rise of general microbiology. Bacteriol. Rev., 13:161-74. 1952 With M. B. Allen. Experiments on bacterial denitrification. I. Bac- teriol., 64:397-412. Bacterial photosynthesis. In: The Enzymes, vol. 2, part 2, eds. I B. Sumner and K. Myrback, New York: Academic Press, pp. 1074-88. With H. Larsen and C. S. Yocum. On the energetics of the photo- syntheses in green sulfur bacteria. J. Gen. Physiol., 36:161-71.

CORNELIS BERNARDUS VAN NIEL 421 With M. B. Allen. A note on Pseudomonas stutzeri. 64:413-22. 1953 I Bacterial., With M. B. Allen and B. E. Wright. On the photochemical reduc- tion of nitrate by algae. Biochim. Biophys. Acta, 12:67-74. Introductory remarks on the comparative biochemistry of micro- organisms. J. Cell. Comp. Physiol., 41(Suppl. 1~: 1 1-38. 1954 The chemoautotrophic and photosynthetic bacteria. Annul Rev. Microbiol., 8:105-32. 1955 Classification and taxonomy of the bacteria and bluegreen algae. In: A Century of Progress in the Natural Sciences 1853-1953, ed. E. L. Kessel, San Francisco: California Academy of Sciences, pp. 89-1 14. On radicalism and conservatism in science. Bacterial. Rev., 19: 1-5. < Natural selection in the microbial world. l. Gen. Microbiol.. 13:201-17. The microbe as a whole. In: Perspectives and Horizons in Microbiology, ed. S. A. Waksman, New Brunswick, N.~.: Rutgers University Press, pp. 3-12. 1956 With T. W. Goodwin and M. E. Sissins. Studies in carotenogenesis. 21. The nature of the changes in carotinoid synthesis in Rho- dospirillum rubrum during growth. Biochem. I., 63:408-12. Phototrophic bacteria: Key to the understanding of green plant photosynthesis, pp. 73-92; Trial and error in living organisms: Microbial mutations, pp. 130-54; Evolution as viewed by the microbiologist, pp. 155-76. In: The Microbe's Contribution to Biol- ogy. A. J. Kluyver and C. B. van Niel. Cambridge: Harvard Uni- versity Press. With G. Milhaud and l. P. Aubert. Etudes de la glycolyse de Zymo- sarcina ventriculi, Ann. Inst. Pasteur, 91:363-68. In memoriam: Professor Dr. Ir. A. I. Kluyver. Antonie van Leeu- wenhoek J. Microbiol. Serol., 22:209-17.

422 BIOGRAPHICAL MEMOIRS 1957 Rhodobacteriineae, pp. 35-67; Propionibacterium, pp. 569-76; Achromatiaceae, pp. 851-53. In: Bergey's Manual of Determina- tive Bacteriology, 7th ea., eds. R. S. Breed, E. G. D. Murray, and N. R. Smith. Baltimore: Williams and Wilkins. Albert Ian Kluyver, 1888-1956.~. Gen. Microbiol., 16:499-521. 1959 Kluyver's contributions to microbiology and biochemistry. In: Albert fan Klayver, His Life and Work, eds. A. F. Kamp. I. W. M. La Riviere, and W. Verhoeven, Amsterdam: North-Holland Pub- lishing Co. and New York: Interscience Publishers, pp. 68-155. With R. Y. Stanier. Bacteria. In: Freshwater Biology, ed. W. T. Ed- mondson, New York: John Wiley & Sons, pp. 16-46. 1962 The present status of the comparative study of photosynthesis. Annul Rev. Plant Physiol., 13: 1-26. With R. Y. Stanier. The concept of a bacterium. Arch. Mikrobiol., 42:17-35. 1963 With L. R. Blinks. The absence of enhancement (Emerson effect) in the photosynthesis of Rhodospir~llum rubrum. In: Studies on Microalgae and Photosynthetic Bacteria, ed. Japanese Society for Plant Physiology, Tokyo: University of Tokyo Press, pp. 297- 307. A brief survey of the photosynthetic bacteria. In: Bacterial Photo- synthes~s, eds. H. Gest, A. San Pietro, and L. P. Vernon, Yellow Springs, Ohio: Antioch Press, pp. 459-67. Ed. C. B. van Niel, Selected Papers of Ernest Georg Pringsheim. New Brunswick, N.~.: Institute of Microbiology, Rutgers University. 1965 On aquatic microbiology today. Science, 148:353. 1966 Microbiology and molecular biology. Q. Rev. Biol., 41: 105-12. Lipmann's concept of the metabolic generation and utilization of

CORNELIS BERNARDUS VAN NIEL 423 phosphate bond energy: A historical appreciation. In: Current Aspects of Biochemical Energetics, eds. N. O. Kaplan and E. P. Kennedy, New York: Academic Press, pp. 9-25. 1967 The education of a microbiologist: Some reflections. Annul Rev. Microbiol., 21: 1-30. 1971 Techniques for the enrichment, isolation, and maintenance of the photosynthetic bacteria. In: Methods in Enzymology, eds. S. P. Colowick and N. O. Kaplan, New York: Academic Press, vol. 23(A), pp. 3-28. 1972 With G. E. Garner and A. L. Cohen. On the mechanism of ballis- tospore discharge. Arch. Mikrobiol., 84:129-40. 1

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Biographic Memoirs Volume 59 contains short biographies of deceased members of the National Academy of Sciences.

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