Culturable diversity and community fatty acid profiling of sulfate-reducing fluidized-bed reactors treating acidic, metal-containing wastewater

Cultivable strains were identified from sulfate-reducing fluidized-bed reactors (FBR) treating acidic metal-containing wastewater. The FBR-communities were further characterized using culture-independent phenotypic markers, phospholipid fatty acid (PLFA) profiling. After morphological screening of 128 bacterial strains and partial sequencing of 55 strains, 17 distinct phylogenetic types were identified and characterized further. A total of 14 and 6 different bacterial strains were isolated from ethanol- and lactate-fed FBRs, respectively. Sequencing of the 16S rRNA gene showed that these strains were affiliated with members of the delta-Proteobacteria, Firmicutes and Bacteroidetes The strains were affiliated with members of the genera Desulfovibrio, Desulfotomaculum, Desulfobulbus, Desulfitobacterium, Clostridium, Caloramator, Oxobacter, and Bacteroides. Many of the strains were only distantly related to previously described species and, thus, may represent novel species or genera. A number of the strains were not detected in previously employed molecular analyses of the FBR communities, and the major component of each FBR as identified in the molecular analyses were not retrieved as cultures in this study. Most of the SRB, and two of the non-SRB utilized ethanol and lactate as a source of carbon and energy, but none of the isolates grew on acetate, an intermediate in the oxidation of ethanol and lactate. PLFA analysis revealed that the FBR community members contained large amounts of saturated fatty acids. Although the PLFA analysis showed some signatures consistent with sulfate-reducing communities, it did not show any substantial difference in the microbial communities between the reactors, an outcome that was quite contrary to the culture-independent phylogenetic analyses.