title: Sulfur compound oxidation and carbon co-assimilation in the haloalkaliphilic sulfur oxidizers Thioalkalivibrio versutus and Thioalkalimicrobium aerophilum.
abstract: Alkaliphilic sulfur-oxidizing bacteria are highly abundant in naturally occurring soda lakes, where they are found both in surface waters and sediments. Here we studied oxidation of sulfide and thiosulfate in batch cultures of Thioalkalimicrobium aerophilum and Thioalkalivibrio versutus, two species that represent different metabolic types, as indicated by the absence or presence of sulfur production during growth, respectively. With thiosulfate, both species showed the expected sulfur oxidation patterns; however, during growth on sulfide, both T. aerophilum and T. versutus produced sulfur as an intermediate. While T. aerophilum likely uses a Sox-type sulfur oxidation pathway, T. versutus appeared to use a combination of some Sox proteins with heterodisulfide reductase complexes, which is supported by gene expression data. Interestingly, intermediate sulfur production by T. versutus occurred when the sulfur source in the medium had been nearly exhausted, which is unlike what has been described for the well-studied Dsr/Sox pathway in phototrophic sulfur bacteria. Inclusion of some carbon sources (acetate, propionate, fructose) slightly enhanced growth of T. versutus and T. aerophilum in batch cultures, suggesting that carbon co-assimilation may be occurring. Our results indicate that sulfur oxidation processes in alkaliphilic sulfur oxidizers are more complex than previously assumed, and that the enzymes involved warrant further study.
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Qld 4072, Australia.
authors.forename: Wee Kiong
authors.initials: WK
authors.lastname: Ang
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Qld 4072, Australia.
authors.forename: Maisarah
authors.initials: M
authors.lastname: Mahbob
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Qld 4072, Australia.
authors.forename: Rabeb
authors.initials: R
authors.lastname: Dhouib
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, St. Lucia, Qld 4072, Australia. Electronic address: u.kappler@uq.edu.au.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kappler
mesh_terms: D061249:Batch Cell Culture Techniques; D002244:Carbon / Q000378:metabolism*; D052837:Chemoautotrophic Growth; D020563:Gammaproteobacteria / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D060106:Lakes / Q000382:microbiology; D010084:Oxidation-Reduction; D010087:Oxides / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology; D013440:Sulfides / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*; D013457:Sulfur Compounds / Q000378:metabolism*
chemical_list: D010087:Oxides; D012336:RNA, Ribosomal, 16S; D013440:Sulfides; D013457:Sulfur Compounds; C405951:sulfur monoxide; D013455:Sulfur; D002244:Carbon
keywords: Chemolithoautotrophy; Haloalkaliphilic bacteria; Sulfur oxidation