Abstract
Members of the genus Thermodesulfovibrio belong to the Nitrospirae phylum and all isolates characterized to date are neutrophiles. They have been isolated from terrestrial hot springs and thermophilic methanogenic anaerobic sludges. Their molecular signatures have, however, also been detected in deep subsurface. The purpose of this study was to characterize and analyze the genome of a newly isolated, facultatively alkaliphilic Thermodesulfovibrio from a 2 km deep aquifer system in Western Siberia, Russia. The new isolate, designated N1, grows optimally at pH 8.5 and at 65°C. It is able to reduce sulfate, thiosulfate or sulfite with a limited range of electron donors, such as formate, pyruvate, and lactate. Analysis of the 1.93 Mb draft genome of strain N1 revealed that it contains a set of genes for dissimilatory sulfate reduction, including sulfate adenyltransferase, adenosine-5′-phosphosulfate reductase AprAB, membrane-bound electron transfer complex QmoABC, dissimilatory sulfite reductase DsrABC, and sulfite reductase-associated electron transfer complex DsrMKJOP. Hydrogen turnover is enabled by soluble cytoplasmic, membrane-linked, and soluble periplasmic hydrogenases. The use of thiosulfate as an electron acceptor is enabled by a membrane-linked molybdopterin oxidoreductase. The N1 requirement for organic carbon sources corresponds to the lack of the autotrophic C1-fixation pathways. Comparative analysis of the genomes of Thermodesulfovibrio (T. yellowstonii, T. islandicus, T. àggregans, T. thiophilus, and strain N1) revealed a low overall genetic diversity and several adaptive traits. Consistent with an alkaliphilic lifestyle, a multisubunit Na+/H+ antiporter of the Mnh family is encoded in the Thermodesulfovibrio strain N1 genome. Nitrogenase genes were found in T. yellowstonii, T. aggregans, and T. islandicus, nitrate reductase in T. islandicus, and cellulose synthetase in T. aggregans and strain N1. Overall, our results provide genomic insights into metabolism of the Thermodesulfovibrio lineage in microbial communities of the deep subsurface biosphere.
Highlights
The genus Thermodesulfovibrio was established in 1994 following the isolation of a novel thermophile, Thermodesulfovibrio yellowstonii, from hydrothermal vent in Yellowstone Lake (Henry et al, 1994)
Groundwater was sampled from a deep artesian borehole, drilled in 1961–1962 for the purpose of oil exploration
No significant hydrocarbon reserves were discovered in the borehole and today it overflows with warm (40–45◦C), slightly brackish groundwater, which is used for small scale commercial and domestic purposes
Summary
The genus Thermodesulfovibrio was established in 1994 following the isolation of a novel thermophile, Thermodesulfovibrio yellowstonii, from hydrothermal vent in Yellowstone Lake (Henry et al, 1994). None of the cultivated Thermodesulfovibrio has been isolated from the deep subsurface. Molecular signatures of this group have, been detected in deep aquifer systems of the Great Artesian Basin, Australia (Kimura et al, 2005), in formation waters and oil from several reservoirs in China (Nazina et al, 2006; Wang et al, 2014; Yang et al, 2016) and in deep granitic groundwater from the Grimsel Test Site, Switzerland (Konno et al, 2013).
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