Hungateiclostridium mesophilum sp. nov., a mesophilic, cellulolytic and spore-forming bacterium isolated from a biogas fermenter fed with maize silage.

In this work, the isolation and characterization of a novel anaerobic, mesophilic and cellulolytic bacterium is described. Comparative analysis of the almost-complete sequence of the 16S rRNA gene showed that the closest relatives were Hungateiclostridium straminisolvens CSK1T (97.53  %) and Hungateiclostridium thermocellum DSM 2360T (95.42  %). Due to physiological and phylogenetic differences from its closest relatives, a new species is proposed. Cells of N2K1T were observed to be rod-shaped, non-motile, spore-forming, Gram-stain-positive and able to adhere directly to cellulose fibre. Cellulolytic activity and optimal growth were observed at 45 °C and neutral pH (optimum, pH 7.5). Of all tested substrates, only filter paper (cellulose) and cellobiose were used for growth. Arabinose, fructose, glucose, lactose, mannitol, mannose, ribose, starch, sucrose, trehalose, xylan and xylose did not support growth. The main fermentation products were acetic acid and isopropanol. The major cellular fatty acids (>5 %) were C16 : 0iso, C16 : 0 DMA and C16 : 0. The type strain, N2K1T, was isolated from a mesophilically operated, lab-scale biogas fermenter fed with maize silage in Freising, Germany in 2017. The genome assembly of strain N2K1T is 4.04 Mbp with a DNA G+C content of 38.36 mol%. The name Hungateiclostridiummesophilum sp. nov. is proposed for the novel organism. Strain N2K1T (=DSM 107956T; =CECT 9704T) represents the type strain of Hungateiclostridiummesophilum sp. nov.