Biomass, bioactivity and biodiversity: microbial ecology of the deep subsurface: analysis of ester-linked phospholipid fatty acids

To understand the ecology of microorganisms in deep subsurface sediments, it is necessary to utilize analyses which look at communities in situ since culturable organisms represent a small fraction of the extant microbiota. Application of the signature lipid biomarker (SLB) technology provides quantitative measures of viable biomass (abundance and distribution), community composition and insight into the nutritional physiological status of the community. With this analysis it was possible to define differences in the communities of different geologic horizons with differing geochemical and geophysical compositions. Although a number of different sites across the continental United States have been studied, the focus of this report is on a single site located in the semi-arid west in New Mexico state where late cretaceous (120–135 Myr) shales and sandstones could be sampled. Sediment cores from this site yielded ester-linked phospholipid fatty acids (PLFA) indicating the presence of viable microbiota as well as diglyceride fatty acids (DGFA) which described the recently dead or non-viable populations of microorganisms. Both the spatial distribution and the nature of PLFA and DGFA were examined under the premises of two hypotheses: (1) that microorganisms in unheated shales would be similar to modern near shore marine sediment organisms and would be absent from heated (volcanic) shales and (2) that different microbial communities would be detected in shales and sandstones as a result of environmental influences and restrictions both at the time of deposition and in subsequent diagenesis.