BY WERNER K. MAAS

BERNARD DAVIS'S MAJOR scientific contributions were in microbial physiology and metabolism. During the late 1940s he discovered an ingenious method for isolating mutants of Escherichia coli that were deficient in individual steps of biosynthetic pathways. His approach was based on the previous work of Beadle and Tatum with the mold Neurospora, but his efficient method permitted him to isolate in one year an arsenal of mutants that in its number and variety surpassed the Neurospora mutants isolated over a previous seven-year period. Furthermore, E. coli was in several ways more suitable for metabolic studies than Neurospora.

Davis used his mutants mainly for working out the steps of biosynthetic pathways. A major advance was his elucidation in the early 1950s of the complete biosynthetic pathway of aromatic amino acids from a common precursor, shikimic acid. Further studies with mutants led also to the clarification of other biosynthetic and catabolic pathways, and to basic findings in the areas of antibiotic action, drug resistance, active transport of metabolites and protein synthesis.

Bernard Davis became a leading figure in biology through his ability to carry out incisive experiments that answered