Validation of signature polarlipid fatty acid biomarkers for alkane‐utilizing bacteria in soils and subsurface aquifer materials

Extractable cell membrane‐derived polarlipid ester‐linked fatty acids (PLFA) obtained from aerated soils gassed with methane or propane and from methane‐ and propane‐oxidizing bacteria isolated from the soils were analyzed by capillary gas chromatography/mass spectrometry. Exposure of aerated soils to methane resulted in the formation of a high proportion of an unusual 18‐carbon mono‐unsaturated PLFA, 18:lw8c. High proportions of this fatty acid biomarker are found in monocultures from this soil grown in minimal media with methane. This PLFA has been previously established as associated with authentic type II methane‐oxidizing bacteria. The microbiota in aerated soils exposed to hydrocarbons containing propane, formed a suite of PLFA characterized by high proportions of a 16‐carbon mono‐unsaturated acid, 16:lw6c, and an 18‐carbon saturated fatty acid with an additional methyl branch at the 10 position, 10 Me 18:0. This PLFA pattern has been detected in several monocultures enriched from the soil with propane‐amended minimal media. The correspondence of high proportions of these unusual mono‐unsaturated PLFA in the isolated monocultures and in situ in the soils after stimulation with the appropriate hydrocarbon is a strong validation of the utility of these biomarkers in defining the community structure of the surface soil microbial community.