Microbial community changes in biological phosphate-removal systems on altering sludge phosphorus content.

Biomarkers (respiratory quinones and cellular fatty acids) and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA genes were used to characterize the microbial community structure of lab-scale enhanced biological phosphate-removal (EBPR) systems in response to altering sludge phosphorus (P) content. All the data suggest that the microbial community structures of sludge samples with a P content between 8 and 12.3% (sludge dry weight) (i.e. good EBPR activity) were very similar, but differed from those with 2% P content (i.e. no EBPR activity). For all samples analysed, ubiquinones Q-8 and Q-10, menaquinone MK-8(H4), and fatty acids C16:0, C16:1 omega9c and C18:1, omega11c were the major components. The dominance of Q-8, Q-10 and MK-8(H4) suggested that large numbers of organisms belonging to the beta and alpha subclasses of the Proteobacteria and the Actinobacteria from the high G+C Gram-positive bacteria, respectively, were present. DGGE analysis revealed at least 7-9 predominant DNA bands and numerous other fragments in each sample. Five major DGGE fragments from each of the 2% and 12% P-containing sludge samples, respectively, were successfully isolated and sequenced. Phylogenetic analysis of the sequences indicated that both 2% and 12% P-containing sludge samples shared three common phylotypes that were separately affiliated with a novel bacterial group from the gamma subclass of the Proteobacteria, two MK-8(H4)-containing actinobacteria previously isolated from the 2% P-containing sludge, and a Caulobacter spp. in the alpha subclass of the Proteobacteria. The phylogenetic analysis also revealed phylotypes unique to both sludge samples. Changes in sludge P content therefore had an effect on the composition and abundance of the predominant microbial populations, though specific phylotypes could not be unequivocally associated with EBPR.