Fight against climate change is taking place on multiple fronts. One of the most relevant is the so-called carbon capture and utilisation technologies (CCUs). CCUs not only reduce greenhouse gas emissions but also convert capture carbon into added-value products.
The Research Group of Molecular Microbial Ecology (geMM) and the Laboratory of Chemical and Environmental Engineering (LEQUIA) of the University of Girona (UdG) have been working for more than a decade on one of such CCUs technologies: microbial electrosynthesis (MES). Microbial electrosynthesis technologies use the electrical properties of some microorganisms (mainly, bacteria and archaea) to reduce carbon dioxide. To operate MES, small amounts of electrical power and water are required, and the production of hydrogen as a key intermediate compound should be controlled. By following this principle, many organic compounds such as methane, butanol, ethanol, or acetate, have already been successfully synthesised at laboratory scale. Still, some limitations hamper the industrial upscale of the process.
Elisabet Perona Vico has applied advanced molecular, electrochemical, and genetic engineering techniques to overcome such limitations. Thus, an electromethanogenic reactor was used to study putative genes taking part in extracellular electron transfer (EET). Microbial community composition analysis through both DNA and cDNA signatures revealed that electromethanogenesis was conducted by Methanobacterium sp. Short-time changes in electron flow (closed and open electric circuits) were used to determine the gene expression levels of [NiFe]-hydrogenases (Eha, Ehb, and Mvh), heterodisulfide reductase (Hdr), coenzyme F420-reducing [NiFe]-hydrogenase (Frh), and hydrogenase maturation protein (Hyp). According to RT-PCR data, suspected mechanisms were not regulated at the transcriptional level.
Another remarkable aspect of Elisabet Perona’s doctoral thesis is the study of microorganisms that could serve as potentially interesting sustainable H2 producers in biocathodes. Particularly, she has studied the biological H2 production in biocathodes operated at -1.0 V vs. Ag/AgCl, using a highly comparable technology and using CO2 as the sole carbon feedstock. Ten different bacterial strains were chosen from genera Rhodobacter, Rhodopseudomonas, Rhodocyclus, Desulfovibrio, and Sporomusa, all described as hydrogen-producing candidates. Eight over ten bacterial strains showed electroactivity and H2 production rates increased significantly (2 to 8-fold) compared to abiotic conditions for two of them (Desulfovibrio paquesii DSM 16681 and Desulfovibrio desulfuricans DSM 642).
Results showed that the application of bacteria-coated cathodes for sustainable H2 production may not be efficient enough to maintain H2 biosynthetic requirements for highly efficient producing strains. Here, we applied genetic engineering tools intending to further increase the H2 production ability of D. paquesii. [Fe]-only hydrogenase and tetraheme cytochrome c3 were selected as genes of interest to be overexpressed in D. vulgaris DSM 644 and D. paquesii DSM 16681. Different conditions and described protocols were tested towards implementing the proper mechanisms to ensure overexpression of the selected genes.
To sum up, Elisabet Perona’s doctoral thesis contributes to a better understanding of the key role of H2 during microbial electrosynthesis and leads to the formulation of several conclusions. First, enhancing the current knowledge of extracellular electron transfer may lead to better control of reductive BES. Second, the required H2 supply for sustainable electrochemical bioprocesses may be provided in a more efficient way using bio-H2 evolving microorganisms. Finally, the thesis corroborates that the application of synthetic biology and defined consortia are new and promising contributions in the METs field. The thesis was directed by Drs Lluís Bañeras (gEMM) and Sebastià Puig (LEQUIA). The dissertation’s defense will take place next Friday 28th January at 11:00h at “Aula Magna” of UdG Faculty of Sciences. Moreover, it can be followed on Microsoft Teams.
Photo: H2 measurements in a bioelectrochemical system.