Physiology of a marine Beggiatoa strain and the accompanying organism Pseudovibrio sp. - a facultatively oligotrophic bacterium

Large filamentous sulfide-oxidizing bacteria are capable of forming huge microbial mats at the oxic-anoxic interface of the sediment surface. The first part of this thesis shows that a subpopulation of Beggiatoa filaments actively migrates into anoxic, sulfidic layers as a reaction to high sulfide fluxes. The reason for this so far unknown migration behavior seems to be excessive storage of reserve compounds. By moving into anoxic regions, aerobic sulfide oxidation is stopped and storage space is emptied by reducing the stored sulfur with carbon reserve compounds. The association of the sulfide-oxidizer and a small heterotrophic bacterium (Pseudovibrio sp.) is investigated in the second part of this thesis. In contrast to the large Beggiatoa sp., the Pseudovibrio sp. is able to grow in pure culture under extremely oligotrophic conditions. Under oligotrophic conditions we found that Pseudovibrio sp. grows on organic contaminations preferentially containing nitrogen.