Anodic microbial community analysis of microbial fuel cells based on enriched inoculum from freshwater sediment.

Abstract: The characterization of anodic microbial communities is of great importance in the study of microbial fuel cells (MFCs). These kinds of devices mainly require a high abundance of anode respiring bacteria (ARB) in the anode chamber for optimal performance. This study evaluated the effect of different enrichments of environmental freshwater sediment samples used as inocula on microbial community structures in MFCs. Two enrichment media were compared: ferric citrate (FeC) enrichment, with the purpose of increasing the ARB percentage, and general enrichment (Gen). The microbial community dynamics were evaluated by polymerase chain reaction followed by denaturing gradient gel electrophoresis (PCR-DGGE) and real time polymerase chain reaction (qPCR). The enrichment effect was visible on the microbial community composition both during precultures and in anode MFCs. Both enrichment approaches affected microbial communities. Shannon diversity as well as β-Proteobacteria and γ-Proteobacteria percentages decreased during the enrichment steps, especially for FeC (p < 0.01). Our data suggest that FeC enrichment excessively reduced the diversity of the anode community, rather than promoting the proliferation of ARB, causing a condition that did not produce advantages in terms of system performance. Graphical abstract: [Figure not available: see fulltext.]

The study of electrochemically active planktonic microbes in microbial fuel cells in relation to different carbon-based anode materials

MFCs (Microbial fuel cells) are bio-electrochemical systems that convert chemical energy into electrical energy by utilizing electrochemically active bacteria.rt-qPCR (Real-time quantitative polymerase chain reaction) assays were used to identify the planktonic bacteria present in the production of electricity in MFCs. The relationship between the bacterial communities with different carbon-based anode materials, such as C-FELT (carbon felt), carbon felt with C-PANI (polyaniline) and C-SADDLES (carbon-coated Berl saddles), were investigated.The distribution of bacteria among the three different MFC anode materials was evaluated. Significant differences were observed for total bacteria (p < 0.01), Geobacter (p < 0.05) and Shewanella (p < 0.05). These differences were generally due to higher bacterial counts in the C-FELT anode MFC. Significant differences in maximum power density (p < 0.001) were also observed; the C-PANI MFC showed the highest maximum power density of 28.5 W/m3 when compared with the C-FELT (4.7 W/m3) and C-SADDLES (4.6 W/m3) MFCs. The greatest number of electrochemically active planktonic microbes was observed in the C-FELT MFC, whereas the C-PANI MFC had the optimum carbon-based anode material

Shape-engineered titanium dioxide nanoparticles (TiO2-NPs): cytotoxicity and genotoxicity in bronchial epithelial cells

The aim of this study was to evaluate cytotoxicity (WST-1 assay), LDH release (LDH assay) and genotoxicity (Comet assay) of three engineered TiO2-NPs with different shapes (bipyramids, rods, platelets) in comparison with two commercial TiO2-NPs (P25, food grade). After NPs characterization (SEM/T-SEM and DLS), biological effects of NPs were assessed on BEAS-2B cells in presence/absence of light. The cellular uptake of NPs was analyzed using Raman spectroscopy. The cytotoxic effects were mostly slight. After light exposure, the largest cytotoxicity (WST-1 assay) was observed for rods; P25, bipyramids and platelets showed a similar effect; no effect was induced by food grade. No LDH release was detected, confirming the low effect on plasma membrane. Food grade and platelets induced direct genotoxicity while P25, food grade and platelets caused oxidative DNA damage. No genotoxic or oxidative damage was induced by bipyramids and rods. Biological effects were overall lower in darkness than after light exposure. Considering that only food grade, P25 and platelets (more agglomerated) were internalized by cells, the uptake resulted correlated with genotoxicity. In conclusion, cytotoxicity of NPs was low and affected by shape and light exposure, while genotoxicity was influenced by cellular-uptake and aggregation tendency