Isolation and characterization of a mixotrophic sulfur-oxidizing Thermus scotoductus

Thermophilic, faculatatively mixotrophic sulfur-oxidizing bacteria were iso lated from a sulfide-rich, neutral hot spring in Iceland. The strain, IT-72 54, used thiosulfate and elemental sulfur as electron donors, oxygen and ni trate as electron accepters, and acetate and other organic compounds as car bon sources, After a few days of growth in the presence of thiosulfate, thi s strain formed sulfur globules. Comparison of intracellular enzymes and he me proteins of heterotrophically and mixotrophically grown cells showed som e differences. The new isolate belonged to Thermus scotoductus because the small subunit (SSU) rRNA gene sequence analysis showed 98.6% sequence simil arity and 84% DNA:DNA reassociation to Thermos scotoductus NMX2 A.1. It is also close to Thermus antranikianii HN3-7, with 98.3% and 79% SSU rRNA sequ ence similarity and DNA:DNA reassociation, respectively. It was also found that both Thermus NMX2 A.1 and T. antranikianii HN3-7 were able to oxidize thiosulfate but that the T. scotoductus type strain SE-1 was not. This is t he first report of Thermus strains that are capable of mixotrophic growth w ith sulfur oxidation.