OCCURRENCE AND TYPES OF THIOBACILLUS‐LIKE BACTERIA IN THE SEA1

Offshore waters and sediments of the Atlantic Ocean and the Black Sea and inshore waters near Woods Hole, Massachusetts, were examined for bacteria resembling Thiobacillus sp., and 136 isolates were obtained by enrichment culture with thiosulfate or elemental sulfur as the energy source. Enrichments for iron‐oxidizing thiobacilli were unsuccessful. Under chemolithotrophic growth conditions, only 19% of the isolates oxidized more than 5% of the thiosulfate supplied in mineral medium, with an increase, moderate decrease, or no change in the pH of the medium. Strains that decreased the p H were proportionately most abundant in inshore water. Thirty‐five percent of the isolates could be cultured on sulfide substrate with a greater yield than on thiosulfate. Seventy‐four percent of the isolates could grow anoxically in thiosulfate mineral medium containing nitrate as the terminal acceptor; only 3 of these produced gas from nitrate. About 95% of all isolates could be grown on organic media. Heterotrophically grown cultures could easily be grown on thiosulfate mineral medium when transferred from organic medium. Apparently the “typical” obligately chemoautotrophic thiobacilli are rare in the marine environment and biological oxidation of reduced sulfur compounds in open ocean areas is largely carried out by facultatively autotrophic bacteria.