CO2 valorization by a new microbiological process

Methane biohydroxylation into methanol by Methylosinus trichosporium OB3b: possible limitations and formate use during reaction

Methane (CH4) hydroxylation into methanol (MeOH) by methanotrophic bacteria is an attractive and sustainable approach to producing MeOH. The model strain Methylosinus trichosporium OB3b has been reported to be an efficient hydroxylating biocatalyst. Previous works have shown that regardless of the bioreactor design or operation mode, MeOH concentration reaches a threshold after a few hours, but there are no investigations into the reasons behind this phenomenon. The present work entails monitoring both MeOH and formate concentrations during CH4 hydroxylation, where neither a gaseous substrate nor nutrient shortage was evidenced. Under the assayed reaction conditions, bacterial stress was shown to occur, but methanol was not responsible for this. Formate addition was necessary to start MeOH production. Nuclear magnetic resonance analyses with 13C-formate proved that the formate was instrumental in regenerating NADH; formate was exhausted during the reaction, but increased quantities of formate were unable to prevent MeOH production stop. The formate mass balance showed that the formate-to-methanol yield was around 50%, suggesting a cell regulation phenomenon. Hence, this study presents the possible physiological causes that need to be investigated further. Finally, to the best of our knowledge, this study shows that the reaction can be achieved in the native bacterial culture (i.e., culture medium containing added methanol dehydrogenase inhibitors) by avoiding the centrifugation steps while limiting the hands-on time and water consumption.

Exploring modes of microbial interactions with implications for methane cycling

Methanotrophs are the sole biological sink of methane. Volatile organic compounds (VOCs) produced by heterotrophic bacteria have been demonstrated to be a potential modulating factor of methane consumption. Here, we identify and disentangle the impact of the volatolome of heterotrophic bacteria on the methanotroph activity and proteome, using Methylomonas as model organism. Our study unambiguously shows how methanotrophy can be influenced by other organisms without direct physical contact. This influence is mediated by VOCs (e.g. dimethyl-polysulphides) or/and CO2 emitted during respiration, which can inhibit growth and methane uptake of the methanotroph, while other VOCs had a stimulating effect on methanotroph activity. Depending on whether the methanotroph was exposed to the volatolome of the heterotroph or to CO2, proteomics revealed differential protein expression patterns with the soluble methane monooxygenase being the most affected enzyme. The interaction between methanotrophs and heterotrophs can have strong positive or negative effects on methane consumption, depending on the species interacting with the methanotroph. We identified potential VOCs involved in the inhibition while positive effects may be triggered by CO2 released by heterotrophic respiration. Our experimental proof of methanotroph-heterotroph interactions clearly calls for detailed research into strategies on how to mitigate methane emissions.

A Comprehensive Review of CO2 Hydrogenation into Formate/Formic Acid Catalyzed by Whole Cell Bacteria

The increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to the use of fossil fuels, pose a significant threat to the environment and necessitate urgent action to mitigate climate change. Carbon capture and utilization technologies that can convert CO2 into economically valuable compounds have gained attention as potential solutions. Among these technologies, biocatalytic CO2 hydrogenation using bacterial whole cells shows promise for the efficient conversion of CO2 into formate, a valuable chemical compound. Although it was discovered nearly a century ago, comprehensive reviews focusing on the utilization of whole-cell bacteria as the biocatalyst in this area remain relatively limited. Therefore, this review provides an analysis of the progress, strategies, and key findings in this field. It covers the use of living cells, resting cells, or genetically modified bacteria as biocatalysts to convert CO2 into formate, either naturally or with the integration of electrochemical and protochemical techniques as sources of protons and electrons. By consolidating the current knowledge in this field, this review article aims to serve as a valuable resource for researchers and practitioners interested in understanding the recent progress, challenges, and potential applications of bacterial whole cell catalyzed CO2 hydrogenation into formate.

CO2 capture and conversion to syngas via dry reforming of C3H8 over a Pt/ZrO2–CaO catalyst

Pt/ZrO2–5CaO could capture 10.3 mmol CO2 g−1 and convert it to syngas completely in C3H8 with little intensive energy swing.