Ruminiclostridium herbifermentans sp. nov., a mesophilic and moderately thermophilic cellulolytic and xylanolytic bacterium isolated from a lab-scale biogas fermenter fed with maize silage.

An anaerobic bacterial strain, designated MA18, was isolated from a laboratory-scale biogas fermenter fed with maize silage. Cells stained Gram-negative and performed Gram-negative in the KOH test. The peptidoglycan type was found to be A1y-meso-Dpm direct. The major cellular fatty acids were C iso, C iso, anteiso and iso DMA as well as a C unidentified fatty acid. Oxidase and catalase activities were absent. Cells were slightly curved rods, motile, formed spores and measured approximately 0.35 µm in diameter and 3.0-5.0 µm in length. When cultivated on GS2 agar with cellobiose, round, arched, shiny and slightly yellow-pigmented colonies were formed. The isolate was mesophilic to moderately thermophilic with a growth optimum between 40 and 48 °C. Furthermore, neutral pH values were preferred and up to 1.2 % (w/v) NaCl supplemented to the GS2 medium was tolerated. Producing mainly acetate and ethanol, MA18 fermented arabinose, cellobiose, crystalline and amorphous cellulose, ribose, and xylan. The genome of MA18 consists of 4 817 678 bp with a G+C content of 33.16 mol%. In the annotated protein sequences, cellulosomal components were detected. Phylogenetically, MA18 is most closely related to DSM 19573 (76.88 % average nucleotide identity of the whole genome sequence; 97.23 % 16S rRNA gene sequence similarity) and can be clustered into one clade with other species of the genus , family , class . Based on morphological, physiological and genetic characteristics, this strain represents a novel species in the genus . Therefore, the name sp. nov. is proposed. The type strain is MA18 (=DSM 109966=JCM 39124).