MARINE THIOBACILLI: II. CULTURE AND ULTRASTRUCTURE

Gram-negative, polar-flagellated bacteria isolated from the Atlantic Ocean using thiosulfate or elemental sulfur as the sole energy source are considered members of the genus Thiobacillus. These cultures require seawater in the medium although they grow optimally when the salinity is reduced to a range of 6.4 to 25.8 p.p.t. There is no growth at 0 salinity and a 25–30% reduction of thiosulfate oxidation in 3 weeks is observed at 18 °C in a salinity of 32.3 p.p.t. The pH of the medium decreased from 7.2 or 5.6 to a final pH of 2–3. One culture decreased the pH to only 5.0 while oxidizing 80% of the thiosulfate. One representative culture, WH-2, was able to oxidize only thiosulfate and elemental sulfur from a series of substrates including tetrathionate, sulfite, sulfur-containing amino acids, and mineral sulfides. This culture is a strict aerobe and did not grow in the presence of 0.01% yeast extract, 2216E, or nutrient broth.The ultrastructure of culture WH-2 indicates that it is very similar to that of Thiobacillus thioosidans. The cells indicate a substantial cell envelope, cytomembranes, electron-dense fibrillar nuclear material, unknown granules, and distinct polyphosphate granules.