How do coal degrading methanogens make biogas? Unravelling central metabolism of Methermicoccus shengliensis
Microbial Ecology and Applied Microbiology
Final Report Abstract
For a long time only bacteria but not archaea were thought to have the potential to grow on methoxylated aromatic compounds, also called methoxydotrophic growth. Only recently the methanogenic archaeon Methermicoccus shengliensis was shown to be capable of methoxydotrophic growth, but nothing was known about its metabolism. In this project, I was able to show by a transcriptomic and proteomic approach that M. shengliensis uses an O- demethylation/methyl transfer (Mto) system that is more related to that of acetogenic bacteria than the methyl transferase system of methylotrophic archaea. With biochemical approaches we were able to show that the methyl group is transferred from the methoxy compound to the corrinoid protein MtoC by the O-demethylase MtoB. We further got strong evidence that MtoA transfers the methyl group to tetrahydromethanopterin instead of coenzyme M which differs from the conventional methanogenic methyl-transfer systems. This discovery might likely lead to an oscillating metabolism in which M. shengliensis disproportionates methoxy groups to CO2 and CH4 in a way that differs from conventional methanogenesis pathways. Next to M. shengliensis, I could demonstrate for the first time that also the hyperthermophilic, non-methanogenic archaeon A. fulgidus can grow on methoxylated aromatic compounds by using a similar bacterial-like O- demethylation/methyl transfer system. In this novel archaeal metabolism A. fulgidus mainly produces CO2 from methoxylated aromatics and uses sulfate as electron acceptor. The growth enhancement of A. fulgidus by using methoxy compounds together with lactate as growth substrate indicates that usage of methoxylated aromatics as co-substrate might also improve the growth of other microorganisms that thrive in environments where methoxylated aromatics are present alongside organic compounds such as lactate. In summary, this project led to a detailed description of the methoxydotrophic growth and metabolism of two archaea which differ in the metabolic pathways they use. The abundance of methoxylated aromatic compounds in the subsurface together with the identification of two methoxydotrophic archaea indicates that those microorganisms might play a so far underestimated role in the global carbon cycle.
Publications
- (2020) Several ways one goal—methanogenesis from unconventional substrates. Appl Microbiol Biotechnol 104: 6839-6854
JM Kurth, HJP Op den Camp, CU Welte
(See online at https://doi.org/10.1007/s00253-020-10724-7)
