Reflections of a microbiologist, or how to learn from the microbes.

This autobiographical chapter summarizes the author's work with a defined mineral medium for fastidious sulfide-oxidizing phototrophic purple and green sulfur bacteria that were known already from Winogradsky's and Lauterborn's descriptions. The pure cultures, isolated from natural mud deposits, revealed interesting new cytological and biochemical features. In the wake of these studies, new anaerobic bacteria with unusual metabolic capacities were isolated and characterized. Ecologically most significant is the dehydrogenation of acetate to carbon dioxide. Electron acceptors are sulfur for the sulfur reducers and sulfate for the new sulfate reducers obtained by Widdel. Thauer and Fuchs showed that a modified TCA-cycle and the new acetyl-CoA:carbon monoxide dehydrogenase pathway operates in the oxidation of acetate. Many aliphatic and aromatic compounds were shown to be completely degradable by marine sulfate reducers. The biogeochemical transformations of the anoxic sulfur cycle are now understood in terms of the capacities of the phototrophic and chemotrophic bacterial species involved in the cycle.