Extracellular Electron Transport-Mediated Fe(III) Reduction by a Community of Alkaliphilic Bacteria That Use Flavins as Electron Shuttles

The biochemical and molecular mechanisms used by alkaliphilic bacterial communities to reduce metals in the environment are currently unknown. We demonstrate that an alkaliphilic (pH > 9) consortium dominated by Tissierella, Clostridium and Alkaliphilus sp. are capable of using iron (Fe(3+)) as a final electron acceptor under anaerobic conditions. Iron reduction is associated with the production of a freely diffusible species that upon rudimentary purification and subsequent spectroscopic, HPLC and electrochemical analysis has been identified as a flavin species displaying properties indistinguishable from riboflavin. Due to the link between iron reduction and the onset of flavin production, it is likely that riboflavin has an import role in extracellular metal reduction by this alkaliphilic community

Sulfur bacteria in wastewater stabilization ponds periodically affected by the ‘red-water’ phenomenon

Several wastewater stabilization ponds (WSP) in Tunisia suffer periodically from the ‘red-water’ phenomenon due to blooming of purple sulfur bacteria, indicating that sulfur cycle is one of the main element cycles in these ponds. In this study, we investigated the microbial diversity of the El Menzeh WSP and focused in particular on the different functional groups of sulfur bacteria. For this purpose, we used denaturing gradient gel electrophoresis of PCR-amplified fragments of the 16S rRNA gene and of different functional genes involved in microbial sulfur metabolism (dsrB, aprA, and pufM). Analyses of the 16S rRNA revealed a relatively high microbial diversity where Proteobacteria, Chlorobi, Bacteroidetes, and Cyanobacteria constitute the major bacterial groups. The dsrB and aprA gene analysis revealed the presence of deltaproteobacterial sulfate-reducing bacteria (i.e., Desulfobacter and Desulfobulbus), while the analysis of 16S rRNA, aprA, and pufM genes assigned the sulfuroxidizing bacteria community to the photosynthetic representatives belonging to the Chlorobi (green sulfur bacteria) and the Proteobacteria (purple sulfur and non sulfur bacteria) phyla. These results point on the diversity of the metabolic processes within this wastewater plant and/or the availability of sulfate and diverse electron donors.BiotechnologyApplied Science