A thermophilic mediatorless microbial fuel cell (ML-MFC) was developed for continuous electricity production while treating artificial wastewater concurrently. A maximum power density of 1030 +/- 340 mW/m2 was generated continuously at 55 degrees C with an anode retention time of 27 min (11 mL h(-1)) and continuous pumping of air-saturated phosphate buffer into the cathode compartment at the retention time of 0.7 min (450 mL h(-1)). Meanwhile, about 80% of the electrons available from acetate oxidation were recovered as current. Denaturing gradient gel electrophoresis (DGGE) and direct 16S-rRNA gene analysis revealed that the bacterial diversity in this ML-MFC system was lower than the inoculum. Direct 16S rDNA analysis showed that the dominant bacteria representing 57.8% of total population in anode compartment was phylogenetically very closely related to an uncultured clone, clone E4. Two sheets of graphite used as the anode showed different dominant bacterial population. For the first time, it is shown that thermophilic electrochemically active bacteria can be enriched to concurrently generate electricity and treat artificial wastewater in a thermophilic ML-MFC.

Aim:  To evaluate the bioenergy generation and the microbial community structure from palm oil mill effluent using microbial fuel cell. Methods and Results:  Microbial fuel cells enriched with palm oil mill effluent (POME) were employed to harvest bioenergy from both artificial wastewater containing acetate and complex POME. The microbial fuel cell (MFC) showed maximum power density of 3004 mW m−2 after continuous feeding with artificial wastewater containing acetate substrate. Subsequent replacement of the acetate substrate with complex substrate of POME recorded maximum power density of 622 mW m−2. Based on 16S rDNA analyses, relatively higher abundance of Deltaproteobacteria (88·5%) was detected in the MFCs fed with acetate artificial wastewater as compared to POME. Meanwhile, members of Gammaproteobacteria, Epsilonproteobacteria and Betaproteobacteria codominated the microbial consortium of the MFC fed with POME with 21, 20 and 18·5% abundances, respectively. Conclusions:  Enriched electrochemically active bacteria originated from POME demonstrated potential to generate bioenergy from both acetate and complex POME substrates. Further improvements including the development of MFC systems that are able to utilize both fermentative and nonfermentative substrates in POME are needed to maximize the bioenergy generation. Significance and Impact of the Study:  A better understanding of microbial structure is critical for bioenergy generation from POME using MFC. Data obtained in this study improve our understanding of microbial community structure in conversion of POME to electricity.

A proteomic analysis of a soil-dwelling, plant growth-promoting Azotobacter vinelandii strain showed the presence of a protein encoded by the hypothetical Avin_16040 gene when the bacterial cells were attached to the Oryza sativa root surface. An Avin_16040 deletion mutant demonstrated reduced cellular adherence to the root surface, surface hydrophobicity, and biofilm formation compared to those of the wild type. By atomic force microscopy (AFM) analysis of the cell surface topography, the deletion mutant displayed a cell surface architectural pattern that was different from that of the wild type. Escherichia coli transformed with the wild-type Avin_16040 gene displayed on its cell surface organized motifs which looked like the S-layer monomers of A. vinelandii. The recombinant E. coli also demonstrated enhanced adhesion to the root surface. Azotobacter vinelandii is a Gram-negative free-living and obligate aerobic soil bacterium. It is well known to be a plant growth-promoting bacterium capable of fixing nitrogen and forming desiccation-resistant cysts under unfavorable growth condition (1, 2). The former activity requires it to house several oxygen-sensitive mechanisms while being an obligate aerobic bacterium (3). A. vinelandii also has characteristics such as production of plant growth hormones and antibiotics (4) as well as industrially important substances such as extracellular polysaccharide (EPS) alginate, poly-␤-hydroxybutyrate (PHB), and siderophore compounds (5).Many diverse genera of nitrogen-fixing bacteria are present in the plant rhizosphere. The effectiveness of their plant growthpromoting activity depends upon the establishment of their cells in the rhizosphere. This interaction depends upon many factors, one of them being plant exudates. As a diazotroph, A. vinelandii provides fixed nitrogen to the plant while acquiring sugars and other nutrients that leak from the roots (6).The complete A. vinelandii genome (GenBank accession number NC_012560) has explained many biochemical pathways and structures of the bacterium (7). It has also revealed hypothetical genes with unannotated functions. The advances in proteomic technology have led to new understanding of and insights into many important proteins and their related mechanisms.Studies have shown that plant-microbe communication is a two-way interaction involving various signal molecules that cause metabolic changes in both organisms (8-10). Nevertheless, there is limited information on the plant-bacterium interaction, especially with the roots and the rhizosphere. In this study, a proteomic approach was successfully used to study the interaction between a root-associated bacterium and rice plant in the rhizosphere (11-13).In this study, a differential proteomic analysis of A. vinelandii ATCC 12837 in response to different conditions and at different locations within the Oryza sativa MR 219 rhizosphere was performed. By two-dimensional gel electrophoresis (2DE) followed by tandem mass spectrometry (MS/MS) analyses, several known and hypothetical p...