Quantification of syntrophic fatty acid-beta-oxidizing bacteria in a mesophilic biogas reactor by oligonucleotide probe hybridization

Small-subunit rRNA sequences were obtained for two saturated fatty acid-bet a-oxidizing syntrophic bacteria, Syntrophomonas sapovorans and Syntrophomon as wolfei LYE, and sequence analysis confirmed their classification as memb ers of the family Syntrophomonadaceae. S, wolfei LYE was closely related to S. wolfei subsp. wolfei, but S. sapovorans did not cluster with the other members of the genus Syntrophomonas, Five oligonucleotide probes targeting the small-subunit rRNA of different groups within the family Syntrophomonad aceae, which contains all currently known saturated fatty acid-beta-oxidizi ng syntrophic bacteria, were developed and characterized. The probes were d esigned to be specific at the family, genus, and species levels and were ch aracterized by temperature of-dissociation and specificity studies, To demo nstrate the usefulness of the probes for the detection and quantification o f saturated fatty acid-beta-oxidizing syntrophic bacteria in methanogenic e nvironments, the microbial community structure of a sample from a full-scal e biogas plant was determined. Hybridization results with probes for syntro phic bacteria-and methanogens were compared to specific methanogenic activi ties and microbial numbers determined with most-probable-number estimates. Most of the methanogenic rRNA was comprised of Methanomicrobiales rRNA,sugg esting that members of this order served as the main hydrogen utilizing mic roorganisms. Between 0.2 and 1% of the rRNA was attributed to the Syntropho monadaceae, of which the majority was accounted for by the genus Syntrophom onas.