Diversity of Nitrogen-Containing Bacteriohopanepolyols: Biomarkers for Aerobic Methane Oxidation in Terrestrial CH4 Seeps

Summary The greenhouse gas CH4 plays an important role in the Earth’s carbon cycle as it actively influences climate change. The aerobic oxidation of CH4 (AMO) plays a key role in oxidizing CH4 before it reaches the atmosphere. AMO can be traced using different lipid biomarkers, specifically bacteriohopanepolyols (BHPs) with nitrogen-containing side chains such as aminotetrol or aminopentol. Soils are one of the largest microbial sinks for atmospheric CH4 but, to date, they have only been investigated for soil-specific BHPs and not AMO-characteristic BHPs. In this study, a new UHPLC-HRMS2 method was applied to investigate the diversity of non-derivatized BHPs in soils near two continuous terrestrial CH4 seeps in Sicily, Italy. The microbial diversity of methanotrophic bacteria was assessed by 16S rRNA gene amplicon sequencing. Overall, our data suggest that AMO-specific BHPs (e.g. aminopentol) in tandem with novel identified composite BHPs such as BHPs with an ethenolamine head group and acylated aminotriol BHPs reveal consistent trends with AMO activity in sampling transects from high to low CH4 availability. Their abundance relatively to common soil-BHPs like adenosylhopanes may potentially be used to reconstruct recent and paleomethanotrophy in terrestrial environments.