Methanol utilization by a novel thermophilic homoacetogenic bacterium, Moorella mulderi sp. nov., isolated from a bioreactor

A thermophilic, anaerobic, spore-forming bacterium (strain TMS) was isolated from a thermophilic bioreactor operated at 65 °C with methanol as the energy source. Cells were gram-positive straight rods, 0.4–0.6 µm×2–8 μm, growing as single cells or in pairs. The temperature range for growth was 40–70 °C with an optimum at 65 °C. Growth was observed from pH 5.5 to 8.5, and the optimum pH was around 7. The salinity range for growth was 0–45 g NaCl l−1 with an optimum at 10 g l−1. The isolate was able to grow on methanol, H2-CO2 (80/20%, v/v), formate, lactate, pyruvate, glucose, fructose, cellobiose and pectin. The bacterium reduced thiosulfate to sulfide. The G+C content of the DNA was 53 mol%. Comparison of 16S rRNA genes revealed that strain TMS is related to Moorella glycerini (96%, sequence similarity), Moorella thermoacetica (92%) and Moorella thermoautotrophica (92%). On the basis of physiological and phylogenetic differences, strain TMS is proposed as a new species within the genus Moorella, Moorella mulderi sp. nov. (=DSM 14980, =ATCC BAA-608).