MIXOTROPHIC AND LITHOHETEROTROPHIC GROWTH OF THE FRESH-WATER FILAMENTOUS SULFUR BACTERIUM BEGGIATOA-LEPTOMITIFORMIS D-402

The functional role of oxidation of reduced sulfur compounds was studi ed in the freshwater bacterium Beggiatoa leptontitiformis D-402. When the bacterium oxidized thiosulfate or tetrathionate in batch culture o n medium with succinate, biomass yields increased 1.7-3.7 times as com pared to organotrophically grown culture. Bacterial cells grown lithoh eterotrophically exhibited high activities of the key enzymes of sulfu r metabolism-sulfite:cytochrome c oxidoreductase and thiosulfate:ferri cyanide oxidoreductase. The presence of rhodanese, thiosulfate reducta se, and tetrathionate oxidase was also demonstrated. Inhibitor analysi s revealed the coupling of sulfur compound oxidation with the function ing of the electron transfer chain (ETC) and energy generation via oxi dative phosphorylation. The AMP-dependent oxidation of thiosulfate by APS reductase, which is linked with substrate phosphorylation, was not found in the cells. The stimulatory effect of rotenone on the cell yi eld and sulfite oxidase activity was revealed. The ability of freshwat er Beggiatoa (B. leptomitiformis D-402) to grow lithoheterotrophically and mixotrophically oxidizing reduced sulfur compounds was demonstrat ed for the first time.