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esis, is the morphological manifestation of the chimera genetic system that evolved from a Thiodendron-type consortium. Each phenomenon we suggest, from free-living bacteria to integrated association, enjoys extant natural analogues.

Study of marine microbial mats revealed relevant bacterial consortia in more than six geographically separate locations. Isolations from Staraya Russa mineral spring 8, mineral spring Serebryani, Lake Nizhnee, mudbaths; littoral zone at the White Sea strait near Veliky Island, Gulf of Nilma; Pacific Ocean hydrothermal habitats at the Kurile Islands and Kraternaya Bay; Matupi Harbor Bay, Papua New Guinea, etc. (Dubinina et al., 1993a) all yielded “Thiodendron latens” or very similar bacteria. Samples were taken from just below oxygen-sulfide interface in anoxic waters (Dubinina et al., 1993a, b). Laboratory work showed it necessary to abolish the genus Thiodendron because it is a sulfur syntrophy. A stable ectosymbiotic association of two bacterial types grows as an anaerobic consortium between 4 and 32°C at marine pH values and salinities. Starch, cellobiose, and other carbohydrates (not cellulose, amino acids, organic acids, or alcohol) supplemented by heterotrophic CO2 fixation provide it carbon. Thiodendron appears as bluish-white spherical gelatinous colonies, concentric in structure within a slimy matrix produced by the consortium bacteria. The dominant partner invariably is a distinctive strain of pleiomorphic spirochetes: they vary from the typical walled Spirochaeta 1:2:1 morphology to large membranous spheres, sulfur-studded threads, gliding or nonmotile cells of variable width (0.09–0.45 µm) and lengths to millimeters. The other partner, a small, morphologically stable vibrioid, Desulfobacter sp., requires organic carbon, primarily acetate, from spirochetal carbohydrate degradation. The spirochetal Escherichia coli-like formic acid fermentation generates energy and food. Desulfobacter sp. cells that reduce both sulfate and sulfur to sulfide are always present in the natural consortium but in far less abundance than the spirochetes. We envision the Thiodendron consortium of “free-living spirochetes in geochemical sulfur cycle” (Dubinina et al., 1993b, p. 456) and spirochete motility symbioses (Margulis, 1993) as preadaptations for chimera evolution. Thiodendron differs from the archaebacterium-eubacterium association we hypothesize; the marine Desulfobacter would have been replaced with a pleiomorphic wall-less, sulfuric-acid tolerant soil Thermoplasma-like archaebacterium. New thermoplasmas are under study. We predict strains that participate in spirochete consortia in less saline, more acidic, and higher temperature sulfurous habitats than Thiodendron will be found.

When “pure cultures” that survived low oxygen were first described [by B. V. Perfil'ev in 1969, in Russian (see Dubinina et al., 1993a, b)] a complex life history of vibrioids, spheroids, threads and helices was attributed to “Thiodendron latens.” We now know these morphologies are

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