Michael Vedel Wegener Kofoed

Biointegrated carbon capture and utilization (BICCU) represents a promising alternative to conventional carbon capture technologies, combining microbial methanogenesis with CO2 capture agents, such as methyl diethanolamine (MDEA), to produce renewable methane from dilute CO2 sources. However, the biotoxicity of these solvents poses a major challenge to the viability of the BICCU approach. This study investigates the biocompatibility and physiological responses ofMethanococcus maripaludis and Methanosarcina barkeri to MDEA, through batch experiments and transcriptomic analysis. Both methanogens exhibited inhibited methane production when exposed to MDEA, with M. barkeri displaying higher sensitivity. M. maripaludis maintained the highest CH4 production rate at 30 mmol/L MDEA, while M. barkeri was almost fully inhibited at this concentration. Transcriptomic analysis revealed upregulation of genes associated with S-layer formation, cell envelope biogenesis, glycosyltransferase activity, and ion transport, alongside downregulation of lysine biosynthesis and secretion system genes. These findings suggest a metabolic trade-off, where cellular energy is reallocated toward stress response mechanisms. Results demonstrate that, while MDEA can be integrated with microorganisms, the exact response will depend on the methanogenic strain. Future research should focus on more biocompatible solvents and the selection of resilient methanogenic strains.

The global consensus for decarbonization is accelerating the shift from a linear fossil-based carbon economy to a sustainable circular model in which CO2 becomes a central carbon resource. Carbon capture and utilization (CCU) technologies are essential to recycle CO2, but the high oxidation number and thermodynamic stability of CO2 restrict most conversion technologies to highly concentrated CO2, imposing large energy penalties for concentrating CO2 using solvent-based capture pathways. Bio-integrated carbon capture and utilization (BICCU) is a promising technology that alleviates this energy penalty by merging capture agent based CO2 capture with simultaneous bio-mediated desorption and conversion in a single bioreactor, enabling cost-effective utilization of diluted CO2 sources. However, the direct coupling of CO2 desorption from capture agents and microbial conversion creates new bioreactor design requirements, which must handle the heterogeneous conditions imposed by the presence of capture agents (methyldiethanolamine), dynamic pH shifts driven by CO2 conversion (7.5–9.2), H2 gas-liquid mass transfer rate limitations, residual dissolved oxygen (0–5 mg L-1), and biologically active conversion zones. Addressing these constraints through dedicated bioreactor research, it was discovered that gas-phase trickle bed reactors were an effective platform for combined CO2 desorption and conversion, in contrast to classical bubble column bioreactor designs. This reactor design was tested in a first-of-its-kind full BICCU process chain, including biofuel combustion, flue gas CO2 capture, and bio-mediated CO2 desorption and conversion into renewable e-methane, reaching a CH4 productivity of 8 L L-1 d-1 on par with more mature biomethanation using O2-free concentrated CO2 streams.

Anthropogenic CO2 emissions from flue gases pose a gigaton-scale challenge, which incremental improvements to conventional CO2 capture technologies alone cannot address. Bio-integrated carbon capture and utilization (BICCU) rethinks classical absorption-based CO2 capture by directly coupling chemical CO2 capture with bio-mediated conversion, eliminating the energy-intensive thermal desorption of conventional CO2 capture. However, the success of coupling capture agents with archaeal biocatalysts is constrained by incompatibility, as most capture agents exhibit antimicrobial properties. Herein, a design framework was developed to integrate capture chemistry with CO2-based biotechnology by combining abiotic CO2 loading, biotic assays, and kinetic modeling to correlate these processes with the physicochemical properties of a broad library of agents. Octanol-water partitioning, topological polar surface area, and hydrophilic groups were identified as key parameters for tuning capture agents toward biocompatibility, as these molecular traits influence hydrophobicity and membrane permeability. Guided by these discoveries, new capture agents can be discovered, as demonstrated by the synthesis of (diethanolamine)3triazine with a standardized biocompatibility of 1078 mMCO2, which is a 6.4-fold increase compared to conventional agents such as melamine of merely 168 mMCO2. These principles establish a blueprint for designing next-generation agents, unlocking bio-mediated CO2 valorization for scalable, low-energy methane production from diluted CO2 sources.

Methanogenesis is a crucial component of Earth’s carbon cycle and a source of methane for biofuel production. The presence of higher energy electron acceptors, such as iron(III) oxides and quinones, is believed to significantly impact methanogenesis. This study investigated the physiological and proteomic responses of the type I Methanosarcina, M. barkeri , to the artificial quinone 9,10-anthraquinone-2,7-disulfonate disodium (2,7-AQDS), using H ₂ /CO ₂ as substrates. Our findings revealed that during 2,7-AQDS reduction, cellular growth ceased. The lack of energy conservation was associated with direct inhibition of both methanogenesis and CO ₂ utilization, corroborated by a significant downregulation of the enzymes involved in this metabolic pathway. Furthermore, the significant upregulation of specific subunits of the reversible Ech hydrogenase suggests that this enzyme redirects electrons from H ₂ towards the most energetically favorable reaction (2,7-AQDS reduction), rather than the reduction of ferredoxin, which is a highly energy-demanding process, essential for initiating the CO ₂ reduction pathway. Additionally, it is conceivable that Ech homologues in other hydrogenotrophic methanogens also participate in the reduction of higher energy-yielding electron acceptors. These findings provide novel insights into how quinones, particularly in their oxidized state, directly impact methanogenesis, thereby influencing both artificial and natural methanogenic environments.

Pig farming is a major contributor to the emissions of greenhouse gases and pollutants. Methane (CH₄), with a global warming potential 27 times that of carbon dioxide (CO₂), accounts for up to 80% of the greenhouse gases at the farm level. Concurrently, pig production is responsible for 15% of the global livestock-related ammonia (NH₃) emissions. Mitigation strategies that are highly effective and environmentally friendly are lacking. Here, we present a novel slurry treatment driven by the biological conversion of glycerol by Limosilactobacillus reuteri with the support of indigenous slurry microbiota activity, leading to the formation of the reuterin system, a broad-spectrum antimicrobial. The in situ production of reuterin reduced CH₄ emissions by up to 95% in pig slurries and lowered CO₂ and NH₃ emissions, depending on the slurry type. Taken together, the microbial conversion of glycerol by L. reuteri holds promise as a biological slurry treatment to mitigate agriculture-related greenhouse and pollutant gas formation.

Acetogenic bacteria are attractive biocatalysts for the conversion of CO ₂ with H ₂ into acetate, as in gas fermentation. Gas fermentation reactors may benefit from biofilm formation, but cell attachment by acetogens is often limited. This study indeed found that the acetogen Sporomusa ovata 2663 was mainly planktonic and aimed to increase its biofilm formation through adaptive laboratory evolution. The adaptation strategy consisted of growing S. ovata on plastic carriers in bottles with a H ₂ :CO ₂ headspace and transferring few carriers to bottles with fresh carriers over eight serial transfers. This procedure resulted in the evolved S. ovata 2663-BF, which had a consistent increased propensity to attach. In heterotrophic growth conditions, four times more cells attached to the bottom of well plates in comparison to the wild type. Moreover, twice as many cells adhered to carriers when grown on H ₂ :CO ₂ . This improved attachment, however, did not lead to higher acetate production rates in simple trickle bed reactors, as the used experimental setup likely stimulated planktonic growth due to a low trickling frequency. Only after some medium replacements to remove planktonic cells, higher gas consumption rates were recorded for the evolved culture. Interestingly, the evolved S. ovata had a relevant point mutation in the gene galU , encoding UDP-glucose pyrophosphorylase, an enzyme involved in the synthesis of extracellular polysaccharides. Overall, this study demonstrates that cell attachment by S. ovata was increased through adaptive laboratory evolution, offering the prospect of investigating the importance of biofilm formation in biofilm-based gas fermentation reactors. IMPORTANCE: Acetogenic bacteria are attractive biocatalysts for the conversion of CO ₂ with H ₂ into acetate, as in gas fermentation and microbial electrosynthesis. Both biotechnologies could benefit from biofilm formation, since biofilm formation retains the catalytic activity inside continuously operated reactors. In addition, biofilm-based gas fermentation reactor systems are advantageous to improve the gas to liquid mass transfer of H ₂ and CO ₂ . Moreover, microbial electrosynthesis benefits from biofilms on cathodes to consume H ₂ as soon as it gets generated. Acetogenic bacteria are however often found to only form thin or sparse biofilms. In the current study, we demonstrated that adaptive laboratory evolution is a useful strategy to increase the biofilm formation capabilities of the acetogen, Sporomusa ovata . The obtained biofilm improved S. ovata is of interest to deepen our fundamental understanding of biofilm formation by acetogens, as well as to assess the importance of biofilm formation for the performance of biofilm-based bioreactors.