Widespread Bathyarchaeia encode a novel methyltransferase utilizing lignin‐derived aromatics

Abstract

Lignin degradation is a major process in the global carbon cycle across both terrestrial and marine ecosystems. Bathyarchaeia, which are among the most abundant microorganisms in marine sediment, have been proposed to mediate anaerobic lignin degradation. However, the mechanism of bathyarchaeial lignin degradation remains unclear. Here, we report an enrichment culture of Bathyarchaeia, named Candidatus Baizosediminiarchaeum ligniniphilus DL1YTT001 (Ca. B. ligniniphilus), from coastal sediments that can grow with lignin as the sole organic carbon source under mesophilic anoxic conditions. Ca. B. ligniniphilus possesses and highly expresses novel methyltransferase 1 (MT1, mtgB) for transferring methoxyl groups from lignin monomers to cob(I)alamin. MtgBs have no homology with known microbial methyltransferases and are present only in bathyarchaeial lineages. Heterologous expression of the mtgB gene confirmed O‐demethylation activity. The mtgB genes were identified in metagenomic data sets from a wide range of coastal sediments, and they were highly expressed in coastal sediments from the East China Sea. These findings suggest that Bathyarchaeia, capable of O‐demethylation via their novel and specific methyltransferases, are ubiquitous in coastal sediments.

Microbial Community Organization during Anaerobic Pulp and Paper Mill Wastewater Treatment

“…In all digesters, the fraction of the total archaeal community consisting of Bathyarchaeia ranges between 10 and 20%. Members of this class have been associated with a variety of functions including methylotrophy, cellulose hydrolysis and fermentation, and reductive acetogenesis. − These archaea have also been associated with lignin degradation , which would explain their high relative abundance in the mill digesters. Pulp mill wastewater contains high concentrations of lignin-derived compounds as a result of the pulping process and the associated separation of lignin from wood.…”