ABSTRACT
The recently described bacterium “
Candidatus
Methylomirabilis oxyfera” couples the oxidation of the important greenhouse gas methane to the reduction of nitrite. The ecological significance of “
Ca
. Methylomirabilis oxyfera” is still underexplored, as our ability to identify the presence of this bacterium is thus far limited to DNA-based techniques. Here, we investigated the lipid composition of “
Ca
. Methylomirabilis oxyfera” to identify new, gene-independent biomarkers for the environmental detection of this bacterium. Multiple “
Ca
. Methylomirabilis oxyfera” enrichment cultures were investigated. In all cultures, the lipid profile was dominated up to 46% by the fatty acid (FA) 10-methylhexadecanoic acid (10MeC
16:0
). Furthermore, a unique FA was identified that has not been reported elsewhere: the monounsaturated 10-methylhexadecenoic acid with a double bond at the Δ7 position (10MeC
16:1Δ7
), which comprised up to 10% of the total FA profile. We propose that the typical branched fatty acids 10MeC
16:0
and 10MeC
16:1Δ7
are key and characteristic components of the lipid profile of “
Ca
. Methylomirabilis oxyfera.” The successful detection of these fatty acids in a peatland from which one of the enrichment cultures originated supports the potential of these unique lipids as biomarkers for the process of nitrite-dependent methane oxidation in the environment.