Acidilobus aceticus gen. nov., sp nov., a novel anaerobic thermoacidophilic archaeon from continental hot vents in Kamchatka

New thermoacidophilic organisms that were able to grow anaerobically on sta rch were isolated from the acidic hot springs of Kamchatka. Strain 1904(T), isolated from a hot spring of the Moutnovski volcano, was characterized in detail. Its cells were regular or irregular cocci that were 1-2 mum in dia meter, non-motile, and had a cell envelope consisting of one layer of subun its. The new organism was a hyperthermophile, growing in the temperature ra nge 60-92 degreesC (with an optimum at 85 degreesC), an acidophile, having the ph range for growth of 2.0-6.0 (with an optimum at 3.8), and an obligat e anaerobe. It fermented starch, forming acetate as the main growth product . Other growth substrates were yeast extract, beef extract and soya extract . Growth on yeast extract, beef extract and soya extract was stimulated by elemental sulfur, which was reduced to H2S. Acetate, arabinose, cellulose, formate, fructose, galactose, glucose, glycine, guar gum, lichenan, malate, maltose, methanol, pectin, pyruvate, propionate, xylan, xylose or a mixtur e of amino acids failed to support growth both in the presence and the abse nce of sulfur. When starch was used as the growth substrate, yeast extract (100 mg l(-1)) was required as a growth factor. The G+C content of the DNA was found to be 53.8 mol%. Comparison of the complete 16S rDNA sequence wit h databases revealed that the new isolate belonged to the kingdom Crenarcha eota. It was not closely related to any described genera (showing sequence similarity below 90.8%) and formed a separate branch of the Crenarchaeota. On the basis of physiological differences and rRNA sequence data, a new gen us - Acidilobus - is proposed, the type species being Acidilobus aceticus s train 1904(T)(= DSM 11585(T)).