| Abstract: | The biomass yield of freshwater filamentous sulfur bacteria of the genus Beggiatoa, when grown lithoheterotrophically or mixotrophically, has been shown to increase 2 to 2.5 times under microaerobic conditions (0.12 mg/l oxygen) as compared to aerobic conditions (9 mg/l oxygen). The activity of the glyoxylate cycle key enzymes have been found to increase two to three times under microaerobic conditions (at an O2 concentration of 2 mg/l), and the activities of the sulfur metabolism enzymes increased three to five times (at an O2 concentration of 0.1-0.5 mg/l). It has also been found that, under microaerobic conditions, thiosulfate was almost completely oxidized to sulfate by the bacteria, without accumulation of intermediate metabolites. At the same time, a 2- to 15-fold decrease in the activities of the tricarboxylic acid cycle enzymes involved in the reduction of NAD and FAD was observed. Reorganization of the respiratory chain after changes in aeration and type of nutrition was also observed. It has been found that, in cells grown heterotrophically, the terminal part of the respiratory chain contained an aa3-type oxidase, whereas, during mixotrophic, lithoheterotrophic, and autotrophic growth, aa3-type oxidase synthesis was inhibited, and the synthesis of a cbb3-type oxidase, which is induced under microaerobic conditions, was activated. The gene of the catalytic subunit CcoN of the cbb3-type oxidase was sequenced and proved to be highly homologous to the corresponding genes of other proteobacteria. |
