The “BioEnergy & Environment” team focus its interests on the bio-activation of small molecules by metalloenzymes and anaerobic micro-organisms. The themes are centred around the study of the energy metabolism of microorganisms capable of metabolising diverse gasses such as CO, CO₂, CH₄, H₂. The model microorganisms will be the two photosynthetic bacteria Rhobobacter capsultatus and Rhodospirillum rubrum and the methanogenic archae Methanococcus maripaludis. Understanding the enzymatic mechanisms involved in these processes as well as the optimisation of catalytic processes for applications in sustainable chemistry are at the heart of the team's concerns

Optimization of biological water-gas shift reaction, a key reaction in the synthesis of green fuels
Syngas (mainly composed of CO, H₂ and CO₂) is an inexpensive and versatile substrate generated from any carbon feedstock, enabling a gradual transition to more sustainable energy, thanks to the development of biomass or waste feedstock gasification. This synthesis gas can be used in many different ways such as the synthesis of liquid fuels, commodity products or gasses (H₂ and bio-methane) However, each syngas application places different demands on its composition. Notably, reaching the accurate H₂/CO ratio is a major requirement via an extensive H₂-enrichment processes. In industry, the water-gas shift reaction (WGSR, CO + H₂O-> CO₂ + H₂) plays a significant role to balance H₂/CO ratio. The successful use of syngas in a diverse range of applications over the decades has also prompted the utilization of anaerobic microorganisms capable of growing with CO and/or H₂ as substrates. Among them, hydrogenogenic carboxydotrophs such as Rhodospirillum rubrum are able to use CO as a sole energy source via the biological WGSR, which has the promise to become a green and cost-effective alternative to the industrial reaction. The biological WGSR is catalyzed by a multiprotein complex constituted of a monofunctional NiFe-carbone monoxide dehydrogenase (CODH), a ferredoxin CooF (Fd) and a CO-induced energy-conserving NiFe-Hydrogenase (ECH). CO is oxidized by CODH, releasing electrons used for the reduction of two protons into dihydrogen, catalyzed by the hydrogenase (an unknown mechanism for creating a transmembrane proton gradient is also proposed). CooF transfers electrons from CODH to ECH. On a fundamental point of view, understanding the different partners involved in microbial CO metabolism, and particularly in WGSR is a challenge. Indeed, the enzymes contain highly complex and oxygen-sensitive metal cofactors. Our project is based on a multidisciplinary approach, using advanced spectroscopic, biochemistry, proteomics, nanotechnology and structural methods in order to understand the biological WGSR at the molecular level and to optimize its efficiency for its potential use in biomass valorization processes.

H₂ photoproduction by Rhodobacter capsulatus
Several methods can be applied to produce green hydrogen starting from renewable resources and includes biological ones and more specifically fermentation. Whereas photofermentation has a much higher theoretical yield than dark fermentation due to light energy assimilation, several limitations both on microbiological and technological aspects still exist that prevent to use the full potential of this process. Using metabolic and enzymatic engineering approaches, R. capsulatus will be optimized to enhance its capability to produce biohydrogen by photo-fermentation. To break engineering limitations and allow a decrease in the cost of the biohydrogen produced, some work will continue on light source optimization (useful wavelength selection) and the possibility of producing the hydrogen directly under pressure will be studied. Indeed, pressurizing the hydrogen which is required for its storage is quite energy demanding especially for the first few bars and this opportunity will constitute a real breakthrough.

Biomethane production from solar energy
Today, biomethane comes from the upgrading of biogas, mainly composed of 50-70% of methane, H₂S and CO₂. It results from the fermentation of biomass by mixed-microbial consortia. At the end of the degradation chain, methanogens produce methane from either acetate or hydrogen and carbon dioxide. Methane-producing microorganisms (or methanogens) are obligate anaerobe, representing a dominant group of Archaea. The main substrates for methanogenesis are carbon dioxide and hydrogen or formate (hydrogenotrophic methanogenesis), acetate (acetoclastic methanogenesis), methanol or methyl amines (methylotrophic methanogenesis). Since methanogens are able to produce efficiently and quantitatively pure methane from hydrogen and carbon dioxide at room temperature and pressure, we focus our attention on the use of pure cultures of Methanococcus maripaludis. The objective is to drive biomethane synthesis from solar energy by interfacing a H2 evolution system with microorganisms that use the generated H₂ as an electron donor for CO₂ reduction

Artificial metalloenzymes for the synthesis of high-added value products
The search for sustainable alternatives to inorganic catalysts has led us to design artificial metalloenzymes. Thanks to its strong expertise in biochemistry and X-ray crystallography, the team has a long-term collaboration with BioCE team at our laboratory on the design of artificial monooxygenases. These biohybrids combine the nickel-binding protein NikA as the protein platform and a series of Ru- and Fe-complexes as active centers for sulfoxidation, aromatic hydroxylation and oxychlorination reactions. Recently, the two groups developed successfully new heterogeneous catalysts using the “cross-linked enzyme crystals” technology on “NikA/Fe complexes” hybrids, leading to remarkable catalyst stability and catalytic properties. In next years, the CLEC technology will be extended to a range of catalytic processes for the production of new products with high-added value in the field of energy and therapeutics, with respect to green chemistry principles.