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Thiohalomonas denitrificans gen. nov., sp. nov. and Thiohalomonas nitratireducens sp. nov., novel obligately chemolithoautotrophic, moderately halophilic, thiodenitrifying Gammaproteobacteria from hypersaline habitats

¹ Winogradsky Institute of Microbiology, Russian Academy of Sciences, Prospect 60-let Octyabrya 7/2, 117811 Moscow, Russia
² Department of Environmental Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands
³ MPI für Terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany

Correspondence
Dimitry Yu. Sorokin
soroc{at}inmi.host.ru
or
D.Y.Sorokin{at}tnw.tudelft.nl

A novel group of moderately halophilic, obligately chemolithoautotrophic, sulfur-oxidizing Gammaproteobacteria was found in sediments of various inland hypersaline lakes and a solar saltern. These bacteria were enriched and isolated with thiosulfate as electron donor and nitrate as electron acceptor at 2 M NaCl. Ten isolates (HLD strains) were long non-motile rods. They grew anaerobically as complete denitrifiers, and aerobically under micro-oxic conditions. Sulfate was the final product of thiosulfate and sulfide oxidation, and nitrite and N₂O were intermediates of nitrate reduction to N₂. The HLD strains grew optimally at pH 7.3–7.8, and at NaCl concentrations of 1.5–2.0 M. On the basis of phenotypic and genetic analysis, the moderately halophilic, thiodenitrifying isolates are proposed to be assigned to a new genus and species, Thiohalomonas denitrificans gen. nov., sp. nov. The type strain is HLD 2^T (=DSM 15841^T=UNIQEM U222^T ). A single strain, HRhD 3sp^T, with vibrio-shaped cells, was obtained from a co-culture capable of complete denitrification of nitrate in the presence of either thiocyanate or thiosulfate as electron donor. It grew anaerobically with thiosulfate, reducing nitrate to nitrite, or under micro-oxic conditions at 1.0–2.5 M NaCl with an optimum at 1.0 M. Strain HRhD 3sp^T was genetically related to the HLD strains at the level of a separate species and is described as Thiohalomonas nitratireducens sp. nov. The type strain is HRhD 3sp^T (=DSM 16925^T=UNIQEM U248^T).

The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences obtained in this study are DQ469580–DQ469581, DQ836238, EF117909–EF117913 and EF455919, and for the nirS gene from strain HLD 2^T, AM492191.

Cytochrome difference spectra of cell-free extract obtained from strain HLD 2^T cells grown anaerobically with nitrate and thiosulfate, and graphs showing the influence of NaCl on anaerobic growth of HLD strains with nitrate and thiosulfate, and on the activity of thiosulfate oxidation by washed cells of strain HLD 2^T grown anaerobically are available with the online version of this paper.

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				D. Yu. Sorokin, T. P. Tourova, G. Muyzer, and G. J. Kuenen Thiohalospira halophila gen. nov., sp. nov. and Thiohalospira alkaliphila sp. nov., novel obligately chemolithoautotrophic, halophilic, sulfur-oxidizing gammaproteobacteria from hypersaline habitats Int J Syst Evol Microbiol, July 1, 2008; 58(7): 1685 - 1692. [Abstract] [Full Text] [PDF]