Biofilm promoted current generation of Pseudomonas aeruginosa microbial fuel cell via improving the interfacial redox reaction of phenazines.

Bacteria biofilm plays a key role in current generation of microbial fuel cells (MFCs), especially for the start-up stage. However, the detailed mechanism of the biofilm promoting the power generation is not very clear so far, especially for those exoelectrogens who rely on the self-excreted electron mediators for extracellular electron transfer. In this work, a biofilm formation inhibitor-sodium houttuyfonate (SH) is used to build a "non-biofilm" anode of Pseudomonas aeruginosa (P. aeruginosa) without affecting the bacteria growth during the MFC operation. According to the comparison results of the "non-biofilm" anode and biofilm-covered anode on current generation, phenazines concentration variation and anodic electrocatalysis, the biofilm on the anode not only provides plenty of bacterial cells for catalysis but also promotes the interfacial phenazine redox reaction through accumulating the self-generated mediators on anode for fast interfacial electron transfer. This work proves that the biofilm assisted electron mediator accumulation will benefit such kind of exoelectrogens to sustain sufficient electron mediators for extracellular electron transfer.

Biodiversity and biogeography of rhizobia associated with common bean (Phaseolus vulgaris L.) in Shaanxi Province.

The biodiversity and biogeography of rhizobia associated with bean in Shaanxi Province were investigated. A total of 194 bacterial isolates from bean nodules collected from 13 sampling sites were characterized based on phylogenetic analyses of the 16S rRNA gene, the housekeeping genes recA, glnII and atpD, and the symbiotic genes nodC and nifH. Fifteen genospecies belonging to the genera Rhizobium, Agrobacterium, Ensifer, Bradyrhizobium and Ochrobactrum were defined among the isolates, with Rhizobium sp. II, Agrobacterium sp. II, E. fredii and R. phaseoli being the dominant groups. Four symbiotic gene lineages corresponding to Rhizobium sp. I, Rhizobium sp. II, R. phaseoli and B. liaoningense were detected in the nodC and nifH sequence analyses, indicating different origins for the symbiotic genes and their co-evolution with the chromosome of the bacteria. Moreover, the Ensifer isolates harbored symbiotic genes closely related to bean-nodulating Pararhizobium giardinii, indicating possible lateral gene transfer from Rhizobium to Ensifer. Correlation of rhizobial community composition with moisture, temperature, intercropping, soil features and nutrients were detected. All the results demonstrated a great diversity of bean rhizobia in Shaanxi that might be due to the adaptable evolution of the bean-nodulating rhizobia subjected to the diverse ecological conditions in the area.

Real-time monitoring of phenazines excretion in Pseudomonas aeruginosa microbial fuel cell anode using cavity microelectrodes.

Phenazines are a kind of metabolites that can mediate extracellular Pseudomonas aeruginosa (P. aeruginosa) cells in microbial fuel cells (MFCs). However, it is still not clear that whether and how the excretion profile of phenazines is affected by the operating MFC. Here, we report a real time analysis approach based on a cavity microelectrode electrochemical sensor to investigate the phenazines excretion behavior of P. aeruginosa during MFC operation. The phenazine concentration increases at first 72 h, reaches a plateau and decreases after 120 h and also shows local dependent variation. It is dependent on the MFC current generation profile but also affect by the biofilm formation. Accordingly, a mechanism about phenazines excretion in MFC anode and the phenazines mediated extracellular electron transfer of the P. aeruginosa anode is proposed. This work provides a novel strategy for self-mediated extracellular electron transfer analysis in the operating MFCs.