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We report almost complete sequence specific 1H, 13C and 15N NMR assignments of an unusual Ca2+-binding protein from Entamoeba histolytica (EhCaBP6) in its apo form as a prelude to its structural and functional characterization.

Bacteria is dynamic biocatalyst which is self-regenerating and sustainable in a bioprocess. The respiration and redox state of bacteria are mainly regulated by various external electron acceptors, and significantly influence to the yield/titer of many biosynthesis and biorefinery processes. The cellular redox state is one of the most important factors to control metabolic fluxes and pathways in bioconversion. Conventional strategies for changing the redox state (e.g., the NAD+/NADH ratio) need to provide external oxidants/reductants, such as oxygen, or chemical reductases/oxidases, and carbon source and hydrogen, which are non-sustainable and frequently produce toxic/inhibitory byproducts. In this respect, electrode-based regulation using bioelectrochemical system (BES), has been highlighted for sustainable bioelectricity generation, and in-situ control of bioconversion of substrates such as glycerol, C1 gases etc. The bioelectrochemical regulation of central metabolic fluxes may also trigger gene and enzyme expression. In this study, the increased productivity of the platform chemicals such as 3-hydroxypropionic acid and 1,3-propanediol by using recombinant Klebsiella pneumoniae and E. coli in BES, will be presented as well as recent progress of BES-based bioconversion. The suggested strategy for bacterial redox state regulation not only improves the productivity and yield/titer, but also provides the opportunity for overcoming thermodynamic imbalances in most of bioprocesses. These results could contribute to further improvements in bioprocesses, and could lead to industrial applications for the biorefinery process.

Microbial electrosynthesis (MES) systems can convert CO2 to acetate and other value-added chemicals using electricity as the reducing power. Several electrochemically active redox mediators can enhance interfacial electron transport between bacteria and the electrode in MES systems. In this study, different redox mediators, such as neutral red (NR), 2-hydroxy-1,4-naphthoquinone (HNQ), and hydroquinone (HQ), were compared to facilitate an MES-based CO2 reduction reaction on the cathode. The mediators, NR and HNQ, improved acetate production from CO2 (165 mM and 161 mM, respectively) compared to the control (without a mediator = 149 mM), whereas HQ showed lower acetate production (115 mM). On the other hand, when mediators were used, the electron and carbon recovery efficiency decreased because of the presence of bioelectrochemical reduction pathways other than acetate production. Cyclic voltammetry of an MES with such mediators revealed CO2 reduction to acetate on the cathode surface. These results suggest that the addition of mediators to MES can improve CO2 conversion to acetate with further optimization in an operating strategy of electrosynthesis processes.

The conversion of C1 gas feedstock, such as carbon monoxide (CO), to useful platform chemicals has attracted considerable interest in industrial biotechnology. One conversion method is electrode-based electron transfer to microorganisms using bioelectrochemical systems (BESs). In this BES system, acetate is the predominant component of various volatile fatty acids (VFAs). To appropriately separate and concentrate the acetate produced, a BES-type electrodialysis cell with an anion exchange membrane was constructed and evaluated under various operational conditions, such as applied external current, acetate concentration, and pH. A high acetate flux of 23.9 mmol/m2∙h was observed under a &minus, 15 mA current in an electrodialysis-based bioelectrochemical system. In addition, the initial acetate concentration affected the separation efficiency and transportation rate. The maximum flux appeared at 48.6 mmol/m2∙h when the acetate concentration was 100 mM, whereas the effects of the initial pH of the anolyte were negligible. The acetate flux was 14.9 mmol/m2∙h when actual fermentation broth from BES-based CO fermentation was used as a catholyte. A comparison of the synthetic broth with the actual fermentation broth suggests that unknown substances and metabolites produced from the previous bioconversion process interfere with electrodialysis. These results provide information on the optimal conditions for the separation of VFAs produced by C1 gas fermentation through electrodialysis and a combination of a BES and electrodialysis.