Halophilic CO2-fixing microbial community as biocatalyst improves the energy efficiency of the microbial electrosynthesis process.

Using saline electrolytes in combination with halophilic CO2-fixing lithotrophic microbial catalysts has been envisioned as a promising strategy to develop an energy-efficient microbial electrosynthesis (MES) process for CO2 utilization. Here, an enriched marine CO2-fixing lithotrophic microbial community dominated by Vibrio and Clostridium spp. was tested for MES of organic acids from CO2. At an applied Ecathode of -1V (vs Ag/AgCl) with 3.5 % salinity (78 mScm-1), it produced 379 ± 53 mg/L (6.31 ± 0.89 mM) acetic acid and 187 ± 43 mg/L (4.05 ± 0.94 mM) formic acid at 2.1 ± 0.30 and 1.35 ± 0.31 mM day-1, respectively production rates. Most electrons were recovered in acetate (68.3 ± 3 %), formate (9.6 ± 1.2 %) besides hydrogen (11 ± 1.4 %) and biomass (8.9 ± 1.65 %). Notably, the bioproduction of organic acids occurred at a high energetic efficiency (EE) of âˆ¼ 46 % and low Ecell of 2.3 V in saline conditions compared to the commonly used non-saline electrolytes (0.5-1 mScm-1) in the reported MES studies with CO2 (Ecell: >2.5 V and EE: <34 %).

Microbial electrosynthesis from carbon dioxide feedstock linked to yeast growth for the production of high-value isoprenoids.

The difficulty in producing multi-carbon and thus high-value chemicals from CO2 is one of the key challenges of microbial electrosynthesis (MES) and other CO2 utilization technologies. Here, we demonstrate a two-stage bioproduction approach to produce terpenoids (>C20) and yeast biomass from CO2 by linking MES and yeast cultivation approaches. In the first stage, CO2 (C1) is converted to acetate (C2) using Clostridium ljungdahlii via MES. The acetate is then directly used as the feedstock to produce sclareol (C20), ß-carotene (C40), and yeast biomass using Saccharomyces cerevisiae in the second stage. With the unpurified acetate-containing (1.5 g/L) spent medium from MES reactors, S. cerevisiae produced 0.32 ± 0.04 mg/L ß-carotene, 2.54 ± 0.91 mg/L sclareol, and 369.66 ± 41.67 mg/L biomass. The primary economic analysis suggests that sclareol and biomass production is feasible using recombinant S. cerevisiae and non-recombinant S. cerevisiae, respectively, directly from unpurified acetate-containing spent medium of MES.

Direct utilization of industrial carbon dioxide with low impurities for acetate production via microbial electrosynthesis.

The present study aimed to demonstrate the utilization of unpurified industrial CO2 with low impurities for acetate production via microbial electrosynthesis (MES) for the first time. In MES experiments with CO2-rich brewery gas, the enriched mixed culture dominated by Acetobacterium produced 1.8 ± 0.2 g/L acetic acid at 0.26 ± 0.03 g/Lcatholyte/d rate and outperformed a pure culture of Clostridium ljungdahlii (1.1 ± 0.02 g/L; 0.138 ± 0.004 g/Lcatholyte/d). The electron recovery in acetic acid was also more for mixed culture (84 ± 13%) than C. ljungdahlii (42 ± 14%). Electrochemical analysis of biocathodes suggested the role of microbial biofilm in improved hydrogen electrocatalysis. In comparative gas fermentation tests, the mixed culture outperformed C. ljungdahlii and produced acetic acid at a similar level with both industrial and pure CO2 feedstocks. These results suggest the robustness and capability of the mixed microbial community for utilizing slightly impure industrial CO2 for bioproduction and presents a major advancement in MES technology.