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Direct interspecies electron transfer (DIET) via conductive materials can provide significant benefits to anaerobic methane formation in terms of production amount and rate. Although granular activated carbon (GAC) demonstrated its applicability in facilitating DIET in methanogenesis, DIET in continuous flow anaerobic reactors has not been verified. Here, evidences of DIET via GAC were explored. The reactor supplemented with GAC showed 1.8-fold higher methane production rate than that without GAC (35.7 versus 20.1 ± 7.1 mL-CH 4 /d). Around 34% of methane formation was attributed to the biomass attached to GAC. Pyrosequencing of 16S rRNA gene demonstrated the enrichment of exoelectrogens (e.g. Geobacter ) and hydrogenotrophic methanogens (e.g. Methanospirillum and Methanolinea ) from the biomass attached to GAC. Furthermore, anodic and cathodic currents generation was observed in an electrochemical cell containing GAC biomass. Taken together, GAC supplementation created an environment for enriching the microorganisms involved in DIET, which increased the methane production rate. [ABSTRACT FROM AUTHOR]

Continuously feeding influent wastewater containing diverse bacterial species to a wastewater treatment activated sludge bioreactor may influence the activated sludge bacterial community temporal dynamics. To explore this possibility, this study tracked influent wastewater and activated sludge bacterial communities by pyrosequencing 16S rRNA genes from four full-scale wastewater treatment plants over a 9-month period. The activated sludge communities showed significantly higher richness and evenness than the influent wastewater communities. Furthermore, the two communities were different in composition and temporal dynamics. These results demonstrate that the impact of the influent wastewater communities on the activated sludge communities was weak. Nevertheless, 4.3–9.3% of the operational taxonomic units (OTUs) detected in the activated sludge were shared with the influent wastewater, implying contribution from influent wastewater communities to some extent. However, the relative OTU abundance of the influent wastewater was not maintained in the activated sludge communities (i.e., weak neutral assembly). In addition, the variability of the communities of the shared OTUs was moderately correlated with abiotic factors imposed to the bioreactors. Taken together, temporal dynamics of activated sludge communities appear to be predominantly explained by species sorting processes in response to influent wastewater communities. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bacterial community compositions were explored in hydrogen fermentation of galactose. [•] Cluster I Clostridium was ubiquitous and predominant in dark fermentation. [•] The abundance of cluster I Clostridium was proportional to hydrogen production. [•] Cluster I Clostridium was the key in hydrogen fermentation of galactose. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical treatment of nitrate (NO3 −), nitrite (NO2 −) and mixtures of nitrate and nitrite was evaluated with microbial catalysts on a cathode in three different bioelectrochemical denitrification systems (BEDS). The removal rates and removal percentage of nitrogen (N) compounds varied during biotic and abiotic operations. The biotic cathode using NO3 −-N as an electron acceptor showed enhanced removal percentages (88%) compared to the operation with NO2 −-N (85%). The simultaneous reduction of NO3 −-N and NO2 −-N occurred in the operation with a mixture of N compounds. The bacterial diversity from the initial inoculum (return sludge) changed at the end of bioelectrochemical denitrification operation after 55 days. The microbial community composition was different depending on the type of electron acceptor. BEDS operation with NO3 −-N and NO2 −-N was enriched with Proteobacteria and Firmicutes respectively. BEDS with a mixture of N electron acceptors showed enrichment with Proteobacteria. There was no clear, distinct microbial community between the cathode biofilm and suspended biomass. [Copyright &y& Elsevier]

Abstract: To investigate the distribution and abundance of spirochaetal communities within anaerobic digesters, pyrosequencing of the 16S rRNA gene was conducted. Phylogenetic analysis identified a cluster which included the majority of core spirochaetal operational taxonomic units (OTUs) and environmental clones but no pure-culture strains. Distribution of the core OTUs demonstrated an importance of local factors in shaping the structure of Spirochaetes. Spirochaetal to bacterial 16S rRNA gene copy numbers varied from 1.3% to 30.0% depending on digester samples. Environmental variables were found to influence the relative abundance of Spirochaetes. In a batch anaerobic digestion experiment testing the response to different substrates, acetate most stimulated the activity of Spirochaetes, suggesting possible acetate oxidation by syntrophic acetate oxidation process. Taken together, the results obtained in this study provides an insight into the ecology of Spirochaetes in anaerobic digesters and a basis for future studies examining ecological function of these bacteria. [Copyright &y& Elsevier]

Air-cathode microbial fuel cells (MFCs) were operated with variation of interspatial distance (0, 3, 6, and 9 mm), and the electrochemical performance and microbial community were comparatively evaluated. In polarization analysis the highest power densities (325 mW/m2) was obtained with an electrode spacing of 6 mm showing high capacitance and low charge transfer resistance. The MFC with 0 mm spacing resulted in much lower power density (53 mW/m2) than the other distances possibly due to high oxygen diffusion from the cathode. To compare the anode bacterial community compositions between biomass attached on the anodic electrodes, high throughput sequencing was performed. The community analyses results revealed that the three different clusters of Geobacter belonging to the Deltaproteobacteria were specifically enriched. The cluster I and II of Geobacter were most abundantly distributed in the 0 mm distanced sample which was exposed to relatively higher dissolved oxygen conditions while that of the cluster III was enriched in the 3, 6, and 9 mm samples. These results suggested that the cluster I and II of Geobacter species might survive better under relatively higher oxygen conditions than the cluster III Geobacter. On the other hand, relatively higher voltage and max power density were generated in the 3, 6, and 9 mm distanced MFC systems, where the cluster III Geobacter was highly enriched conditions. These results also suggested that the cluster III Geobacter might efficiently generate higher voltage and maximum power density than the other Geobacter clusters under oxygen limited conditions in air-cathode MFC system. [ABSTRACT FROM AUTHOR]

In this study, microbial responses of a continuous hydrogen reactor fed with galactose have been investigated. Process disturbances reduced H 2 production performance as well as large fluctuations in microbial diversity. The peak values of the hydrogen yield (HY) was not influenced greatly during the steady state period, and accounted as 2.01 ± 0.05 and 2.14 ± 0.03 mol/mol galactose added , while hydraulic retention time (HRT) was at 12 and 8 h, respectively. Microbial community analysis via 454 pyrosequencing revealed that functional redundancy following changes in the microbial community distribution led to the stability of the fermentation performance. The butyrate to acetate (B/A) ratio well correlated with changes in the microbial community. The energy generation rate and energy yield resulted in the peak values of 134 kJ/L-d and 612 kJ/mol added . [ABSTRACT FROM AUTHOR]