C-13-NMR Study of propionate metabolism by sludges from bioreactors treating sulfate and sulfide rich wastewater

Applications of nuclear magnetic resonance (NMR) to study a variety of phys iological and biochemical aspects of bacteria with a role in the sulfur cyc le are reviewed. Then, a case-study of high resolution C-13-NMR spectroscop y on sludges from bioreactors used for treating sulfate and sulfide rich wa stewaters is presented. C-13-NMR was used to study the effect of sulfate an d butyrate on propionate conversion by mesophilic anaerobic (methanogenic a nd sulfate reducing) granular sludge and microaerobic (sulfide oxidizing) f locculant sludge. In the presence of sulfate, propionate was degraded via t he randomising pathway in all sludge types investigated. This was evidenced by scrambling of [3-C-13]propionate into [2-C-13]propionate and the format ion of acetate equally labeled in the C-1 and C-2 position. In the absence of sulfate, [3-C-13]propionate scrambled to a lesser extend without being d egraded further. Anaerobic sludges converted [2,3-C-13]propionate partly in to the higher fatty acid 2-methyl[2,3-C-13]butyrate during the simultaneous degradation of [2,3-C-13]propionate and butyrate. [4,5-C-13]valerate was a lso formed in the methanogenic sludges. Up to 10% of the propionate present was converted via these alternative degradation routes. Labeled butyrate w as not detected in the incubations, suggesting that reductive carboxylation of propionate does not occur in the sludges.