Abstract
Microbiology of a hypersaline oil reservoir located in Central Africa was investigated with molecular and culture methods applied to preserved core samples. Here we show that the community structure was partially acquired during sedimentation, as many prokaryotic 16S rRNA gene sequences retrieved from the extracted DNA are phylogenetically related to actual Archaea inhabiting surface evaporitic environments, similar to the Cretaceous sediment paleoenvironment. Results are discussed in term of microorganisms and/or DNA preservation in such hypersaline and Mg-rich solutions. High salt concentrations together with anaerobic conditions could have preserved microbial/molecular diversity originating from the ancient sediment basin wherein organic matter was deposited.
Highlights
Subsurface environments harbor 1/10 to 1/3 of global living biomass, playing an important role in biogeochemical cycling of elements[1,2]
Expected strict anaerobes are found essentially from the Illumina sequencing where they account for a larger part of the diversity (27.6%) than in the clone library (8.7%)
As expected when considering the number of reads, Illumina sequencing showed a greater diversity than the clone library
Summary
Subsurface environments harbor 1/10 to 1/3 of global living biomass, playing an important role in biogeochemical cycling of elements[1,2]. Subsurface oil-bearing reservoir rocks have been extensively studied during the last century with respect to the critical economic value of hydrocarbons. Biodegradation of organic matter in sedimentary rocks contributes to the biogeochemical cycling of carbon[1] and strongly impacts the quality and exploitation of hydrocarbons[1]. Oil reservoirs are nutrient-depleted environments, especially lacking of phosphorus and nitrogen. They contain an excess of reduced electron donors (hydrocarbons) but a shortage of electron acceptors (e.g., nitrate, oxygen...) and are considered as anaerobic environments[5,6,7]. We characterized the indigenous microbiota of a hypersaline oil reservoir by molecular and cultural analyzes of rock samples, rather than from fluid samples (e.g. production fluid from well heads of oil producing wells) possibly affected by greater exogenous microbial contamination[8]. The core was collected from an onshore oil reservoir in Central Africa, before oil exploitation and any fluid injection
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