Thermovenabulum gondwanense sp. nov., a thermophilic anaerobic Fe(III)-reducing bacterium isolated from microbial mats thriving in a Great Artesian Basin bore runoff channel

Abstract

A strictly anaerobic, thermophilic bacterium, designated strain R270(T), was isolated from microbial mats thriving in the thermal waters (66 degrees C) of a Great Artesian Basin bore (registered no. 17263) runoff channel. Cells of strain R270(T) were straight to slightly curved rods (3.50-6.00x0.75-1.00 microm) that stained Gram-positive, but possessed a Gram-negative cell-wall ultrastructure. Strain R270(T) grew optimally in tryptone-yeast extract-Casamino acids medium at 65 degrees C (growth temperature range between 50 and 70 degrees C) and at pH 7.0 (growth pH range between 6.0 and 9.0). In the presence of 0.02 and 0.10 % yeast extract, pyruvate and Casamino acids were the only substrates fermented from a wide spectrum of substrates tested. Fe(III), Mn(IV), thiosulfate and elemental sulfur were used as electron acceptors in the presence 0.2 % yeast extract, but not sulfate, sulfite, nitrate, nitrite or fumarate. Growth of strain R270(T) increased in the presence of Fe(III), which was reduced in the presence of peptone, tryptone, Casamino acids, amyl media, starch, pyruvate, H(2) and CO(2), but not in the presence of acetate, lactate, propionate, formate, benzoate, glycerol or ethanol. Growth and Fe(III) reduction were inhibited by chloramphenicol, streptomycin, tetracycline, penicillin, ampicillin and 2 % NaCl (w/v). The DNA G+C content of strain R270(T) was 41+/-1 mol% (T(m)) and phylogenetic analysis of the 16S rRNA gene indicated that this isolate was closely related to Thermovenabulum ferriorganovorum DSM 14006(T) (similarity value of 96.1 %) within the family 'Thermoanaerobacteraceae', class 'Clostridia', phylum 'Firmicutes'. On the basis of the phylogenetic distance separating the two, together with differences in a number of key phenotypic characteristics, strain R270(T) represents a novel species of the genus Thermovenabulum, for which the name Thermovenabulum gondwanense sp. nov. is proposed; the type strain is R270(T) (=KCTC 5616(T)=DSM 21133(T)).