Methanotrophy and methanogenesis are central to the Earth's methane balance. The origins of both C1 transfer chemistry reactions are still unknown. Genomic analysis suggests that a compelte set of genes encoding the enzymes of the CBB cycle are present in the Verrucomicrobiae Methylacidiphilum fumariolicum, as reported in Khadem et al., J Bact 2011. This suggest that these methanotrophs may be able to fix CO2, probably using CH4 mainly as an energy source. The authors demonstrate that M. Fumariolicum strain SolV is able to grow using only CH4. Additionally, phylogenetic analysis of RuBiscCO showed that the verrucomicrobial enzyme formed a distinct group in the phylogenetic tree. Additionally, the authors suggest that the verruco RuBiscCO is most likely solubles in those bacteria, and not included in carboxysomes as in cyanobacteria and other nitrifying bacteria. Additional information like gene arrangement suggest that the Methylacidiphilum RuBisCO has
"medium to low affinity for CO2, indicating an adaptation to environments with medium to high CO2 but with O2 present."
The conclusions speak for themselves:
"M. fumariolicum strin SolV is an autotrophic methanotroph. It fixes CO2 via the CVV cycle, with CH4 as the energy source. It uses a non-carboxysoe-associated RuBisCO, in agreement with a high requirement for CO2. RuBisCOs in verrucomicrobial methanotrophs form a new group most closely related to type IC."
The authors postulate that RuBisCO of the verrucomicrobial methanotrophs represents a new type of form I RuBisCO.
