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Abstract

Sulphate-reducing bacteria (SRB), or more generally speaking sulphate-reducing prokaryotes (SRP), are terminal oxidizers in the natural recycling of bio-organic compounds to CO2 in anoxic environments, in particular in marine sediments. SRP play this geochemically important role because they make use of a globally abundant electron acceptor, sulphate (in seawater up to 28 mM), and possess numerous degradative (oxidative) capacities with respect to electron donors. The study of the degradative potentials of SRP via de novo enrichment (including direct counting) and isolation from natural samples has been of interest over some decades and formed the basis for our knowledge of the phylogenetic diversity of SRP. Common electron donors and carbon sources of SRP are the low-molecular mass products from the primary anaerobic (fermentative) breakdown of polysaccharides, proteins, lipids and other substances of dead biomass. Several of the involved degradative capacities, for instance complete oxidation or the channelling of branched-chain fatty acids or aromatic compounds into the central metabolism, require special enzymatic reactions (for overview see Rabus et al., 2000) which are not encountered in fermentative bacteria. The study of such and other metabolic capacities in SRP has led to the recognition of principles of general importance or heuristic value in our understanding of the biochemistry and energetics of anaerobes.