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

An extremely thermophilic, xylanolytic, spore-forming and strict anaerobic bacterium DTU01(T) 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(25°C) 7, with a maximum growth rate of 0.1 h-1. DNA G+C content was 34.2 mol %. Strain DTU01(T) could ferment arabinose, cellobiose, fructose, galactose, glucose, inulin, lactose, mannose, melibiose, pectin, starch, sucrose, xylan, yeast extract and xylose, but not cellulose, Avicel®, mannitol, inositol, glycerol, acetate, lactate, ethanol, butanol or peptone.

Ethanol was the major fermentation product and a maximum yield of 1.39 mol of ethanol per mol xylose was achieved when sulphite was added to the cultivation medium. Thiosulphite, but not sulphate, nitrate or nitrite, could be used as electron acceptor. On the basis of 16S rRNA gene sequence similarity, strain DTU01(T) was shown to be closely related to Thermoanaerobacter mathranii A3(T), T. italicus Ab9(T) and T. thermocopriae JT3-3(T), with 98-99% similarity.

Despite this, the physiological and phylogenetic differences (DNA G+C content, substrate utilization, electron acceptors, phylogenetic distance, isolation site) allow for the proposal of strain DTU01(T) as a new species within the genus Thermoanaerobacter, for which the name Thermoanaerobacter pentosaceus sp. nov. is proposed, with the type strain DTU01(T) (DSM 25963 = KCTC 4529).