Characteristics and phylogenetic analysis of the facultative anaerobic dissimilatory azoreducing bacteria from activated sludge

Physiologically distinct facultative anaerobic microorganisms were isolated and investigated for their ability to oxidize different substrates with azo compounds as a terminal electron acceptor. Four strains of dissimilatory azoreducing bacteria (DARBs), isolated from activated sludge of a textile-printing wastewater treatment plant, could reduce azo compound by coupling oxidation of several of electron donors. Different strains preferred specific electron donor for azoreduction, such as hydrogen, formate or lactate. Evolutionary relationships among these DARBs were examined by phylogenetic analysis of 16S rDNA sequences. Members of the genera Citrobacter (AzoR-1), Acinetobacter (AzoR-3), and Pseudomonas (AzoR-9) formed a monophyletic group within the gamma subdivision of the class Proteobacteria, which was closely related to the member of the previously described Shewanella decolorationnis S12 that obtained its energy for growth by dissimilatory azoreduction process. The genus Bacillus (AzoR-6) made up a distinct branch within the Firmicutes cluster. The results of this study expanded the limited number of microbial isolates that are known to be capable of dissimilatory azoreduction and demonstrated that the ubiquity of azoreduction coupling with hydrogen or organic acids as an electron donor.