Growth and antioxidant activity of Desulfotomaculum acetoxidans DSM 771 cultivated in acetate or lactate containing media.

Three independent 28 or 32-day stationary cultures of Desulfotomaculum acetoxidans DSM 771 strain were carried out under anoxic conditions in acetate or lactate-containing media. The acids were the sole carbon and energy sources in these media. During cultivation the turbidity (for calculation of cell division index) and hydrogen sulfide contents were determined in culture broth and reduced glutathione and protein concentrations were assayed in culture broth supernatant. In these three successive cultures, the bacterium initially grew much faster on lactate than on acetate. However, after two weeks of culture this difference disappeared and in fact the growth rate was higher on acetate than on lactate. The level of H2S formed (product of the dissimilatory pathway of sulfate reduction) demonstrated that this pathway was more effective when lactate was a carbon source and the average H2S concentration was from over 3-fold to about 9-fold greater in lactate than in acetate cultures. Also GSH (glutathione, product of the assimilatory sulfate reduction pathway) average level was about 2-fold higher in lactate-grown cultures. The high negative values of the correlation coefficients between GSH and O2 levels, especially during the first 4 days of cultivation, indicate that GSH is a very important antioxidizing extracellular agent of D. acetoxidans. The rapid increase in GSH level, preceding the release of H2S, indicates the metabolic priority of the assimilation pathway of sulfate reduction. For both carbon sources the highest coefficient of correlation was found between protein and H2S levels. These results suggest that hydrogen sulfide is bound by proteins (which contain cysteinyl residues) secreted by D. acetoxidans cells. Indicated way of H2S bounding could result in its accumulation. This coefficient of correlation increased gradually in the successive cultures. The ratio of H2S concentration to protein concentration increased gradually in the successive cultures, too.