Species composition of cultivated and noncultivated bacteria from short filaments in an Icelandic hot spring at 88 degrees C

Samples of short pink-grayish filaments were collected from a hot spring in the Hengill area in southwestern Iceland at 85-88 degreesC, pH 6.9 and 1.7 mg/L sulfide. The species composition was studied by cloning and sequencin g small subunit rRNA genes obtained by PCR amplifications from mat DNA. Usi ng 98% sequence similarity as a cutoff value, a total of 5 bacterial operat ional taxonomic units (OTUs) and 6 archaeal OTUs were detected among 68 bac terial clones and 97 archaeal clones. Database matching showed that 80.5% o f the archaeal sequences were 99% similar to Pyrobaculum islandicum and 14. 5% were closest to the Korarchaeota clone sequence SRI306. About 87% of the bacterial sequences had the closest database match (99%) to the clone sequ ence SRI48 but were also found to be 99% identical with hydrogen-oxidizing strains previously isolated in this laboratory from hot springs in the same region. Out of 7 Thermus sequences, 4 were 100% identical to T. scotoductu s NMX2 A.1 but 3 represented a new uncultivated Thermus species. Four diffe rent media, varying in organic nutrients and phosphate composition were use d to isolate 81 aerobic thermophilic heterotrophs. Four isolates were Bacil lus spp; but out of 77 Thermus isolates, 42 belonged to T. scotoductus and 35 to T. brockianus, T. scotoductus seemed to be preferably isolated on med ia low in nutrients and phosphate, whereas for T. brockianus it was the opp osite. The T. scotoductus clones and isolates had 99-100% sequence similari ty to each other. No T. brockianus sequences were found in the bacterial cl one library.