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Ultramicrobacteria (UMB) that can pass through a 0.22 µm filter are attractive because of their novelty and diversity. However, isolating UMB has been difficult because of their symbiotic or parasitic lifestyles in the environment. Some UMB have extracellular electron transfer (EET)-related genes, suggesting that these symbionts may grow on an electrode surface independently. Here, we attempted to culture from soil samples bacteria that passed through a 0.22 µm filter poised with +0.2 V vs. Ag/AgCl and isolated Cellulomonas sp. strain NTE-D12 from the electrochemical reactor. A phylogenetic analysis of the 16S rRNA showed 97.9% similarity to the closest related species, Cellulomonas algicola, indicating that the strain NTE-D12 is a novel species. Electrochemical and genomic analyses showed that the strain NTE-D12 generated the highest current density compared to that in the three related species, indicating the presence of a unique electron transfer system in the strain. Therefore, the present study provides a new isolation scheme for cultivating and isolating novel UMB potentially with a symbiotic relationship associated with interspecies electron transfer.

Strain AS-1 was isolated from laboratory-scale activated sludge collected in Japan. This strain not only grows on rich medium, including R2A medium, but also forms colonies on medium lacking organic matter other than agar (water agar), indicating it could be used as a eurytrophic recombinant host in material production processes. Here, we present a draft genome sequence of Enterobacter sp. AS-1, which consists of a total of 24 contigs containing 5,207,146 bp, with a GC content of 55.64%, and comprising 4,921 predicted coding sequences. Based on 16S rRNA gene sequence analysis, strain AS-1 was designated as Enterobacter sp. AS-1.

An aerobic, oligotrophic, Gram-positive, non-sporulating, motile, rod-shaped, palladium-leaching bacterial strain, Deinococcus sp. KR-1, was previously isolated from pond water collected in Japan. This strain grew at 10 °C to 40 °C (optimum 30 °C), at pH 4.5 to 11.5 (optimum pH 8.0), and in the presence of 2.0% NaCl. Its major cellular fatty acids were C15: 1ω6 and C16 : 1ω7c. The quinone system was menaquinone 8. Multilocus sequence analysis based on partial sequences of four housekeeping genes (atpD, dnaA, gyrB and rpoB) showed that branching of Deinococcus sp. KR-1 was distant to those of Deinococcus type strains. The genome average nucleotide identity value between strain KR-1 and its closest related Deinococcus type strain was less than 95.69%. Based on its phenotypic, chemotaxonomic and phylogenetic data, strain KR-1 (= HUT-8138T = KCTC 33977T) can be considered a novel species within the genus Deinococcus with the proposed name Deinococcus kurensis sp. nov.

Methanogens capable of accepting electrons from Fe

Methanogens capable of accepting electrons from Fe0 cause severe corrosion in anoxic conditions. In previous studies, all iron-corrosive methanogenic isolates were obtained from marine environments. However, the presence of methanogens with corrosion ability using Fe0 as an electron donor and their contribution to corrosion in freshwater systems is unknown. Therefore, to understand the role of methanogens in corrosion under anoxic conditions in a freshwater environment, we investigated the corrosion activities of methanogens in samples collected from groundwater and rivers. We enriched microorganisms that can grow with CO2/NaHCO3 and Fe0 as the sole carbon source and electron donor, respectively, in ground freshwater. Methanobacterium sp. TO1, which induces iron corrosion, was isolated from freshwater. Electrochemical analysis revealed that strain TO1 can uptake electrons from the cathode at lower than −0.61 V vs SHE and has a redox-active component with electrochemical potential different from those of other previously reported methanogens with extracellular electron transfer ability. This study indicated the corrosion risk by methanogens capable of taking up electrons from Fe0 in anoxic freshwater environments and the necessity of understanding the corrosion mechanism to contribute to risk diagnosis.

In this study, the microbial community for denitrification in the down-flow hanging sponge (DHS) reactor was estimated by batch experiment and microbial community analysis. Sludge retained from the DHS reactor, which conducts single-stage nitrification-denitrification, was collected into a series of vials as seed sludge for the batch experiment. Nitrate, nitrite, and nitrous oxide were added as nitrogen sources for each vial series. Sodium acetate solution was added to each vial series as a carbon source. At the beginning of the batch experiment, nitrous oxide was accumulated from only the nitrite-fed series (NO2 series). Approximately 50% of reduced nitrate was accumulated as nitrite in the nitrate-fed series (NO3 series). After two weeks of cultivation, nitrous oxide began to accumulate in the NO3 series without nitrite accumulation. Nitrous oxide accumulation was not confirmed in the NO3 series after 15 days of cultivation. During the batch experiment, the predominant denitrifying bacteria changed from Alicycliphilus to Thauera in the NO3 series. By contrast, the nitrous oxide producer Propionibacterium and the nitrous oxide reducer Staphylococcus increased in the NO2 series only. Thus, nitrite accumulation was considered to be a key factor for nitrous oxide emission in the DHS reactor. In addition, it was suggested that both nitrifying and denitrifying bacteria contributed to prevention of nitrite accumulation in the DHS reactor.