Spirochaeta isovalerica sp. nov., a Marine Anaerobe That Forms Branched-Chain Fatty Acids as Fermentation Products

Four strains of obligately anaerobic spirochetes were isolated from marine intertidal mud. These strains grew to yields of 2 × 108 to 6 × 108 cells per ml in chemically defined media containing glucose, amino acids or NH4Cl, sulfide, vitamins, and inorganic salts. These spirochetes required relatively high levels of Na+ for growth and utilized carbohydrates but not amino acids as growth substrates. Glucose was fermented to CO2, H2, ethanol, and acetate. These four strains also formed the branched-chain fatty acids isovalerate, 2-methylbutyrate, and isobutyrate as fermentation products of l-leucine, l-isoleucine, and l-valine, respectively. The adenosine 5′-triphosphate generated via fermentation of these amino acids was expended by the spirochetes to prolong survival during periods of growth substrate starvation. The deoxyribonucleic acids of the four strains contained 63.6 to 65.6 mol% guanine plus cytosine. We concluded that these four strains are representatives of a new species, for which we propose the name Spirochaeta isovalerica; the type strain of this species is strain MA-2 (= DSM 2461).