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 CSK1(T) (97.53 %) and Hungateiclostridium thermocellum DSM 2360(T) (95.42 %). Due to physiological and phylogenetic differences from its closest relatives, a new species is proposed. Cells of N2K1(T) 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 degrees 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 C(16:0)iso, C-16:0 DMA and C-16:0. The type strain, N2K1(T), was isolated from a mesophilically operated, lab-scale biogas fermenter fed with maize silage in Freising, Germany in 2017. The genome assembly of strain N2K1(T) is 4.04 Mbp with a DNA G+C content of 38.36 mol%. The name Hungateiclostridium mesophilum sp. nov. is proposed for the novel organism. Strain N2K1(T) (=DSM 107956(T); =CECT 9704(T)) represents the type strain of Hungateiclostridium mesophilum sp. nov.