Alkaliphilus crotonatoxidans sp nov., a strictly anaerobic, crotonate-dismutating bacterium isolated from a methanogenic environment

Two bacterial strains were isolated from methanogenic butyrate-oxidizing mixed cultures. The cells were straight to slightly curved, Gram-positive rods that were motile by means of multiple flagella and formed endospores. Growth was observed in the temperature range 15-45 degreesC (optimum 37 degreesC) and pH range 5.5-9.0 (optimum pH 7.5). The novel isolates were strictly anaerobic chemo-organotrophs capable of utilizing yeast extract, peptone, tryptone and a variety of sugars and organic acids, but not glucose. None of the accessory electron acceptors tested (elemental sulfur, thiosulfate or fumarate) improved growth, except crotonate, which was dismutated to T butyrate and acetate. The G + C content of the DNA of one of the isolates, strain B11-2(T), was 30.6 mol%. Phylogenetic analysis based on 16S rDNA sequence similarity between strain B11-2(T) and some other strictly anaerobic, spore-forming bacteria indicated that the novel isolates represented a species in cluster XI within the low-GC; Gram-positive bacteria, being most closely related to Alkaliphilus transvaalensis JCM 10712(T). DNA-DNA relatedness between strain B11-2(T) and A. transvaalensis JCM 10712(T) was 21 %. On the basis of physiological and molecular properties, and cellular fatty acid and cell wall compositions, the novel isolates are proposed to represent a novel species of the genus Alkaliphilus, for which the name Alkaliphilus crotonatoxidans is proposed (type strain B11-2(T) = AS 1.2897(T) = JCM 11672(T)).