Abstract
Hydrogenotrophic methanogenic archaea are efficient H2 utilizers, but only a few are known to be able to utilize CO. Methanothermobacter thermoautotrophicus is one of the hydrogenotrophic methanogens able to grow on CO, albeit about 100 times slower than on H2 + CO2. In this study, we show that the hydrogenotrophic methanogen Methanothermobacter marburgensis, is able to perform methanogenic growth on H2/CO2/CO and on CO as a sole substrate. To gain further insight in its carboxydotrophic metabolism, the proteome of M. marburgensis, grown on H2/CO2 and H2/CO2/CO, was analyzed. Cultures grown with H2/CO2/CO showed relative higher abundance of enzymes involved in the reductive acetyl-CoA pathway and proteins involved in redox metabolism. The data suggest that the strong reducing capacity of CO negatively affects hydrogenotrophic methanogenesis, making growth on CO as a sole substrate difficult for this type of methanogens. M. marburgensis appears to partly deal with this by up-regulating co-factor regenerating reactions and activating additional pathways allowing for formation of other products, like acetate.
Highlights
Methanogenesis from hydrogen, acetate, methanol, or methanethiols is a relatively well-studied process (Thauer et al, 2008)
The carbon monoxide dehydrogenase (CODH) complex is in almost all cases associated with an acetyl-CoA synthase (ACS) complex (Techtmann et al, 2012), suggesting it mainly plays a role in the assimilatory metabolism
The slight, but significant, increase in CO-oxidation activity observed in the Cell free extract (CFE) of H2/CO2/CO grown cultures compared to the CFE of H2/CO2 grown cells suggests that more COoxidizing enzymes are present
Summary
Methanogenesis from hydrogen, acetate, methanol, or methanethiols is a relatively well-studied process (Thauer et al, 2008). Syngas-driven carboxydotrophic methanogenesis can be considered as an alternative to biogas production via anaerobic digestion. About 10–25% of the biomass consists of lignin, which is difficult to degrade biologically and can even prevent degradation of degradable biopolymers such as hemicellulose (Daniell et al, 2012; Jönsson and Martín, 2016). Biomass-derived biogas contains a fraction of 25–45% CO2 (De Mes et al, 2003) and needs to be subsequently upgraded to bio-methane before injection in the gas grid is possible. Via the syngas route a higher substrate conversion yield can be achieved, and by increasing the H2 content of the gas substrate a CO2-free end product can be obtained in one process step
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