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Application of quantitative methods for microbial biomass, community structure, and nutritional status to the subsurface samples collected with careful attention to contamination reveals the presence of a group of microbes. The microbiota is sparse by several measures of biomass compared with that present in surface sediments and soils. The community structure, as characterized by the patterns of ester-linked fatty acids from the phospholipids, shows an absence of long-chain polyenoic fatty acids typical of microeukaryotes and high proportions of fatty acids typical of bacteria. Subsurface samples contain a higher proportion of glycerol teichoic acids than surface samples. Microbes in uncontaminated subsurface sediments show nutritional stress as evidenced by high levels of poly-β-hydroxybutyrate and extracellular polysaccharides. The proportions of ester-linked phospholipid fatty acids show distinctive differences between surface and subsurface, between subsurface sandy clay and limestone, and between two sites of subsurface sandy clay as shown using stepwise discriminant analysis. Contamination increased the microbial biomass, shifted the community to a more gram-negative bacterial consortium, and induced growth as evidenced by phospholipid fatty acid biosynthesis.
Smith et al. (Sat,) studied this question.
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