Identification of sulfate reducers andsyntrophobactersp. in anaerobic granular sludge by fatty‐acid biomarkers and 16S rRNA probing

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Abstract
The sulfate‐reducing bacterial sludge population in anaerobic bioreactors, treating different types of wastewater in the presence or absence of sulfate, was evaluated by polar‐lipid fatty acid (PLFA) analyses, and by 16S rRNA dot‐blot hybridizations using specific 16S rRNA‐targeted oligonucleotide probes for sulfate reducers and Syntrophobacter sp. The 16S rRNA dot blot hybridizations were useful for estimating the relative amount of sulfate reducers in the sludge. The PLFA profiles of the sludge were usefid to obtain a quick general impression of the total bacterial sludge composition, but were less suitable for an accurate characterization and quantification of the sulfate‐reducing population in the sludge. This was due to the lack of selective biomarkers for these bacteria. The combined results of the PLFA analysis and 16S rRNA dot‐blot hybridizations showed that the presence of sulfate reducers in the sludge was not dependent on the presence of sulfate in the wastewater. This may be explained by the syntrophic and/or fermentative capacities of some sulfate reducers in the absence of sulfate. Desulfobulbus sp. were important in reactors with carbohydrates and/or volatile fatty acids containing wastewater. These bacteria could play a role in proionate degradation in these reactors. Desulfobacter sp. did not seem to be important for acetate degradation in any of the sulfate‐fed reactors. In the acetate and sulfate‐fed reactor, Desulfotomaculum acetoxidans‐like bacteria seemed to play a role in acetate degradation.