Influence of sulfite on acetate metabolism in Sulfitobacter pontiacus growing in continuous culture

The influence of increasing sulfite loading on the organotrophic metabolism of the marine lithoheterotrophic sulfite-oxidizing bacterium Sulfitobacter pontiacus was studied using an acetate-limited continuous culture. During the adaptation of S. pontiacus to increasing sulfite concentrations, essent ial changes were observed at different levels of the acetate metabolism inc luding the acetate uptake system, the activities of acetate-dependent respi ration and ATP synthesis, and repression of the activity and synthesis of a cetate-catabolizing enzymes of the TCA cycle. These adaptational changes re sulted in a shift in the acetate metabolism towards more efficient carbon a ssimilation due to utilization of sulfite as an additional source of energy . The data obtained explain the mechanism of mixotrophic growth of S. ponti acus and the need for a long adaptation period of growth at low sulfite con centrations before the bacterium starts to grow at high sulfite loading.