Thermoanaerobacter pentosaceus sp. nov., an anaerobic, extremely thermophilic, high ethanol-yielding bacterium isolated from household waste

Abstract

An extremely thermophilic, xylanolytic, spore-forming and strictly anaerobic bacterium, strain DTU01T, was isolated from a continuously stirred tank reactor fed with xylose and household waste. Cells stained Gram-negative and were rod-shaped (0.5–2 µm in length). Spores were terminal with a diameter of approximately 0.5 µm. Optimal growth occurred at 70 °C and pH 7, with a maximum growth rate of 0.1 h−1. DNA G+C content was 34.2 mol%. Strain DTU01Tcould ferment arabinose, cellobiose, fructose, galactose, glucose, lactose, mannitol, mannose, melibiose, pectin, starch, sucrose, xylan, yeast extract and xylose, but not cellulose, Avicel, inositol, inulin, glycerol, rhamnose, acetate, lactate, ethanol, butanol or peptone. Ethanol was the major fermentation product and a maximum yield of 1.39 mol ethanol per mol xylose was achieved when sulfite was added to the cultivation medium. Thiosulfate, but not sulfate, nitrate or nitrite, could be used as electron acceptor. On the basis of 16S rRNA gene sequence similarity, strain DTU01Twas shown to be closely related toThermoanaerobacter mathraniiA3T,Thermoanaerobacter italicusAb9TandThermoanaerobacter thermocopriaeJT3-3T, with 98–99 % similarity. Despite this, the physiological and phylogenetic differences (DNA G+C content, substrate utilization, electron acceptors, phylogenetic distance and isolation site) allow for the proposal of strain DTU01Tas a representative of a novel species within the genusThermoanaerobacter, for which the nameThermoanaerobacter pentosaceussp. nov. is proposed, with the type strain DTU01T( = DSM 25963T = KCTC 4529T = VKM B-2752T = CECT 8142T).