ABSTRACT
Microbial biomass and community structure are determined in terms of universally distributed lipid biomarkers which are characteristic of all cells. A determination of the total ester-linked phospholipid fatty acid (PLFA) content provides a quantitative measure of the viable or potentially viable biomass. The ratio of 3-hydroxyalkanoic acids/PLFA indicated that with the increase in biomass and changes in community composition, a portion of the extant microbiota was experiencing unbalanced growth. In studies of the origins of deep subsurface microbes it is important to be as sure as possible that organisms isolated from deep subsurface cores are truly representative of the extant microbiota. In terms of community composition, the subsurface microbiota was characterized by a greater proportion of Gram-positive and Gram-negative anaerobic bacteria, as compared to surface soils or to estuarine sediments. Surface soils and subsurface sediments, even those collected from near the surface, contained distinctive characteristics which were identified with the signature lipid biomarker analyses.
