• Sciences de l'environnement/Biodiversité et Ecologie
  

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.

Two novel strictly anaerobic bacteria, strains Bs105(T) and Bs107(T), were isolated from a deep aquifer-derived hydrocarbonoclastic community. The cells were rod-shaped, not motile and had terminal spores. Phylogenetic affiliation and physiological properties revealed that these isolates belong to two novel species of the genus Desulfotomaculum. Optimal growth temperatures for strains Bs105(T) and Bs107(T) were 42 and 45 degrees C, respectively. The estimated G+C content of the genomic DNA was 42.9 and 48.7 mol%. For both strains, the major cellular fatty acid was palmitate (C-16 : 0). Specific carbon fatty acid signatures of Gram-positive bacteria (iso-C-17 : 0) and sulfate-reducing bacteria (C(17 : 0)cyc) were also detected. An insertion was revealed in one of the two 16S rRNA gene copies harboured by strain Bs107(T). Similar insertions have previously been highlighted among moderately thermophilic species of the genus Desulfotomaculum. Both strains shared the ability to oxidize aromatic acids (Bs105(T) : hydroquinone, acetophenone, paratoluic acid, 2-phenylethanol, trans-cinnamic acid, 4-hydroxybenzaldehyde, benzyl alcohol, benzoic acid 4-hydroxybutyl ester; Bs107(T) : ortho-toluic acid, benzoic acid 4-hydroxybutyl ester). The names Desulfotomaculum aquiferis sp. nov. and Desulfotomaculum profundi sp. nov. are proposed for the type strains Bs105(T) (= DSM 24088(T) = JCM 31386(T)) and Bs107(T) (= DSM 24093(T) = JCM 31387(T)).