Isolation of Electrochemically Active Bacteria from an Anaerobic Digester Treating Food Waste and Their Characterization.

Studies have used anaerobic-digester sludge and/or effluent as inocula for bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs), for power generation, while limited studies have isolated and characterized electrochemically active bacteria (EAB) that inhabit anaerobic digesters. In the present work, single-chamber MFCs were operated using the anaerobic-digester effluent as the sole source of organics and microbes, and attempts were made to isolate EAB from anode biofilms in MFCs by repeated anaerobic cultivations on agar plates. Red colonies were selected from those grown on the agar plates, resulting in the isolation of three phylogenetically diverse strains affiliated with the phyla Bacillota, Campylobacterota and Deferribacterota. All these strains are capable of current generation in pure-culture BESs, while they exhibit different electrochemical properties as assessed by cyclic voltammetry. The analyses of their cell-free extracts show that cytochromes are abundantly present in their cells, suggesting their involvement in current generation. The results suggest that anaerobic digesters harbor diverse EAB, and it would be of interest to examine their ecological niches in anaerobic digestion.

Shewanella oneidensis MR-1 as a bacterial platform for electro-biotechnology.

The genus Shewanella comprises over 70 species of heterotrophic bacteria with versatile respiratory capacities. Some of these bacteria are known to be pathogens of fishes and animals, while many are non-pathogens considered to play important roles in the global carbon cycle. A representative strain is Shewanella oneidensis MR-1 that has been intensively studied for its ability to respire diverse electron acceptors, such as oxygen, nitrate, sulfur compounds, metals, and organics. In addition, studies have been focused on its ability as an electrochemically active bacterium that is capable of discharging electrons to and receiving electrons from electrodes in bioelectrochemical systems (BESs) for balancing intracellular redox states. This ability is expected to be applied to electro-fermentation (EF) for producing value-added chemicals that conventional fermentation technologies are difficult to produce efficiently. Researchers are also attempting to utilize its electrochemical ability for controlling gene expression, for which electro-genetics (EG) has been coined. Here we review fundamental knowledge on this bacterium and discuss future directions of studies on its applications to electro-biotechnology (EB).

Enhanced electricity generation in rice paddy-field microbial fuel cells supplemented with iron powders.

Microbial fuel cells installed in rice paddy fields (RP-MFCs) are able to serve as on-site batteries for operating low-power environmental sensors. In order to increase the utility and reliability of RP-MFCs, however, further research is necessary for boosting the power output. Here we examined several powdered iron species, including zero valent iron (ZVI), goethite, and magnetite, for their application to increasing power outputs from RP-MFCs. Soil around anodes was supplemented with either of these iron species, and RP-MFCs were operated for several months during the transplanting and harvesting. It was found that power outputs from RP-MFCs supplemented with ZVI were more than double the outputs from control (not supplemented with iron species) and other RP-MFCs, even after iron corrosion was ceased, and the maximum power density reached 130 mW/m2 (per projected area of the anode). Metabarcoding of 16S rRNA gene amplicons suggested that several taxa represented by fermentative and exoelectrogenic bacteria were substantially increased in MFCs supplemented with ZVI. Results suggest that ZVI lowers oxidation/reduction potential around anodes, activates anaerobic microbes involved in the conversion of organic matter into electricity and increases power output from RP-MFCs.

C-mannosylation of R-spondin3 regulates its secretion and activity of Wnt/ß-catenin signaling in cells.

R-spondin3 (Rspo3) is a secreted protein, which acts as an agonist of canonical Wnt/ß-catenin signaling that plays an important role in embryonic development and homeostasis. In this study, we focused on C-mannosylation, a unique type of glycosylation, of human Rspo3. Rspo3 has two putative C-mannosylation sites at Trp(153) and Trp(156) ; however, it had been unclear whether these sites are C-mannosylated or not. We demonstrated that Rspo3 was C-mannosylated at both Trp(153) and Trp(156) by mass spectrometry. Using C-mannosylation-defective Rspo3 mutant-overexpressing cell lines, we found that C-mannosylation of Rspo3 promotes its secretion and activates Wnt/ß-catenin signaling.

N-glycosylation of R-spondin1 at Asn137 negatively regulates its secretion and Wnt/ß-catenin signaling-enhancing activity.

N-glycosylation is a post-translational protein modification with a wide variety of functions. It has been predicted that R-spondin1 (RSPO1) is N-glycosylated, although this remains unknown. The present study identified that RSPO1 was N-glycosylated at Asn137, and that N-glycosylation of RSPO1 negatively influenced its secretion and enhancing effect on Wnt/ß-catenin signaling. In vitro treatment with peptide-N-glycosidase F increased the electrophoretic mobility of RSPO1. Furthermore, treatment of wild-type (wt) RSPO1-overexpressing HT1080 cells with tunicamycin (TM), which inhibits N-glycosylation, resulted in a significant reduction in the molecular weight of RSPO1. However, TM treatment had no effect in the RSPO1 mutant whereby the Asn137 residue was replaced by Gln (N137Q). These results demonstrated for the first time that RSPO1 is N-glycosylated at Asn137. RSPO1 is a secreted protein that has Wnt/ß-catenin signaling-enhancing activity and is expected to have therapeutic applications. The role of N-glycosylation in RSPO1 was evaluated by conducting comparative experiments with wt and N137Q RSPO1, which revealed that the N137Q mutant increased the secretion and Wnt/ß-catenin signaling-enhancing effect of RSPO1, compared with wt RSPO1. These results suggest that N-glycosylation of RSPO1 has a negative influence on its secretion and Wnt/ß-catenin signaling-enhancing effect.