Single-chamber microbial fuel cells (MFCs), inoculated with anaerobic sludge and continuously run with two kinds of organic wastewater influents, were systemically investigated. The diversity of microbes, determined by 16S rDNA analysis, was analyzed on three anodes under different conditions. One anode was in a closed circuit in synthetic wastewater containing glucose. The other two anodes, in open or closed circuits, were fed effluent from an anaerobic reactor treating starch wastewater. The chemical oxygen demand (COD) removal efficiency was about 70%, and the exported voltages were about 450 mV. The 16S rDNA molecular clones of microbes on anode surfaces showed significant changes in Eubacterial structure under different conditions. γ-Proteobacteria and the high G+C gram-positive groups were predominant in the synthetic wastewater, while ε-Proteobacteria predominated in the anaerobic reactor effluent. Known exoelectrogenic bacterial species composition also changed greatly depending on substrate. On the artificial substrate, 28% of the bacterial sequences were affiliated with Aeromonas, Pseudomonas, Geobacter, and Desulfobulbus. On the anaerobic effluent, only 6% were affiliated with Geobacter or Clostridium. Because only a few exoelectrogenic bacteria from MFCs have been directly isolated and studied, we compared the community structures of two bacterial anodes, in open and closed circuits, under the same substrate of anaerobic effluent in order to identify additional exoelectrogenic bacterial strains. Alcaligenes monasteriensis, Comamonas denitrificans, and Dechloromonas sp. were found to be potential exoelectrogenic bacteria worthy of further research.

An understanding of bacterial community composition is a fundamental goal of identifying ecological efficiency caused by Microcystis bloom in aquatic system. In this study, we employed bar-coded 454 pyrosequencing approach to investigate the bacterial community variation during a Microcystis water bloom in Guanting Reservoir, Beijing. More than 140,000 sequences were generated and assigned to 7133 operational taxonomic units (OTUs) which belong to 18 phyla through Ribosomal Database Pyrosequencing (RDP) database. Microcystis was detected at low abundance in July then broke out and became the exclusive dominant genus in September. Meanwhile, bacteria composition changed dramatically after the Microcystis water bloom reflected by the decrease of bacteria abundance, diversity and evenness indices. The classify results indicated that dominant species in July were Pelagibacter, Haliscomenobacter, Rhodobacter and Fluviicola. In September, Methylotenera, Flavobacterium and Methylophilus were the dominant genera. It is worth noticing that all the dominant genera in July was more or less related to nitrogen and phosphorus cycling while in September, dominant genera Flavobacterium was reported as Microcystis lysing bacterium and may be a symptom of the coming postbloom phase of Microcystis water bloom in Guanting Reservoir.