Archaeoglobus fulgidus and Thermotoga elfii, Thermophilic Isolates from Deep Geothermal Water of the Paris Basin

Abstract

Thermophilic anaerobic microorganisms with the ability to reduce sulfur compounds (e.g., sulfate and/or thiosulfate) were isolated from water samples collected from about 2000 meters depth at in situ temperatures of 70°C in a geothermal well from the Paris Basin (France). Chemical and isotopic analyses show that microbial sulfate reduction occurred in the samples. Two strains were characterized by both DNA/DNA hybridization and 16S rRNA gene sequence analysis, which indicated that they are most closely related to Thermotoga elfii, a thiosulfate-reducing bacterium, and Archaeoglobus fulgidus, a sulfate- and thiosulfate-reducing archaeon. Besides thiosulfate reduction using H₂ as energy source, both isolates are shown to be able to retrieve energy from H₂/Fe(III), a metabolic capability of importance in a deep biosphere context. It is suggested that T. elfii and A. fulgidus could be used, either as pure culture or as a consortium, in future laboratory studies aiming at better understanding microbial iron (III) and sulfate/thiosulfate reduction, hydrogen production/consumption, as well as the effect of microorganisms on the evolution of CO₂ in deep aquifers. The present work examines numerous culture conditions and demonstrates that in spite of similarities in phylogenetic/genetic characteristics and in growth conditions, there are significant phenotypic differences between the isolated archaeal strain and the type strain of A. fulgidus. These differences, evidenced by a proteomic study, should be taken into account and could be useful parameters to be studied in the deep aquifers by geomicrobiological laboratories.

Keywords:

• geothermal water
• thermophiles
• anaerobes
• deep ecosystem
• proteomic analysis
• deep biosphere

We would like to thank Vanessa Meiter and Elodie Francezon for technical assistance, Danielle Moinier and Régine Lebrun (IBSM, Proteomic Analysis Center of Marseille, France supported by Marseille-Nice Genopole) for performing the MALDI-TOFanalysis. The manuscript was strongly improved, thanks to the work of two anonymous reviewers.

Notes

¹N°: spot number as shown in Figure 4.

²The sequence coverage represents the % of the combined peptide masses covering the indicated sequence.

³ID: identification by MS in a database of coding genes for the A. fulgidus genome.

⁴Identification and annotated function if applicable.