REFLECTIONS OF A MICROBIOLOGIST, OR HOW TO LEARN FROM THE MICROBES

This autobiographical chapter summarizes the author's work with a defi ned mineral medium for fastidious sulfide-oxidizing phototrophic purpl e and green sulfur bacteria that were known already from Winogradsky's and Lauterborn's descriptions. The pure cultures, isolated from natur al mud deposits, revealed interesting new cytological and biochemical features. In the wake of these studies, new anaerobic bacteria with un usual metabolic capacities were isolated and characterized. Ecological ly most significant is the dehydrogenation of acetate to carbon dioxid e. Electron acceptors are sulfur for the sulfur reducers and sulfate f or the new sulfate reducers obtained by Widdel. Thauer and Fuchs showe d that a modified TCA-cycle and the new acetyl-CoA:carbon monoxide deh ydrogenase pathway operates in the oxidation of acetate. Many aliphati c and aromatic compounds were shown to be completely degradable by mar ine sulfate reducers. The biogeochemical transformations of the anoxic sulfur cycle are now understood in terms of the capacities of the pho totrophic and chemotrophic bacterial species involved in the cycle.