NOVEL EUBACTERIA ABLE TO GROW ON CARBON-DISULFIDE

Four eubacterial strains able to grow on carbon disulfide (CS,) as sole energy substrate were isolated from soil and leaves of the CS2-producing tree Quercus lobata. Three of the isolates (strains KS1, KS2, and KL1) were gram-negative, facultatively methylotrophic and heterotrophic, and capable of growth on a wide range of inorganic and organic sulfur compounds. Biochemical and physiological properties differed slightly among the three strains, but all are proposed to be novel Thiobacillus species. Growth yields on CS, in batch and chemostat culture ranged from 3.3g dry wt/mol CS2 (batch) to a maximum growth yield (Y-max) of 11.1g dry wt/mol (chemostat). Chemostat data for two of the strains growing autotrophically on thiosulfate gave Y-max values of 7.4 and 7.1g dry wt/mol, which fall within the range observed with thiobacilli. The three new Thiobacillus strains had DNA containing 39.8 (KS2), 47.8 (KS1), and 50.5 (KL1) mol% G+C. All three were unusual in being able to grow not only on thiosulfate (aerobically or with denitrification), but also on CS2, carbonyl sulfide, and methylated sulfides as sole energy substrates, and one was unique in being able to grow also on substituted thiophenes. They are the first organisms described to be capable of anaerobic growth with denitrification on CS2. The fourth isolate (strain KL2) was gram-positive, non-motile and nonspore-forming, with 39.0 mol% G+C. It had a restricted range of sulfur-containing growth substrates, could not grow methylotrophically or on autotrophic substrates other than CS2, and is not yet classifiable. These organisms extend the range of eubacteria known to be capable of CS2 breakdown and demonstrate that several types of facultatively chemolithotrophic bacteria, able to grow exclusively on CS2, are associated with a CS2-producing plant.