Clostridium muellerianum sp. nov., a carbon monoxide-oxidizing acetogen isolated from old hay

An acid/alcohol-producing, Gram-stain-positive, obligately anaerobic, rod-shaped, non-motile, non-spore forming acetogen, designated as strain P21^T, was isolated from old hay after enrichment with CO as the substrate. Spores not observed even after prolonged incubation (30 days). Phylogenetic analysis of the 16S rRNA gene sequence of strain P21^T showed it was closely related to Clostridium carboxidivorans DSM 15243^T (97.9%), Clostridium scatologenes DSM 757^T (97.7 %) and Clostridium drakei DSM 12750^T (97.7 %). The genome is 5.6 Mb and the G+C content is 29.4 mol%. Average nucleotide identity between strain P21^T, C. carboxidivorans, C. scatologenes and C. drakei was 87.1, 86.4, 86.4 %, respectively. Strain P21^T grew on CO:CO₂, H₂:CO₂, l-arabinose, ribose, xylose, fructose, galactose, glucose, lactose, mannose, cellobiose, sucrose, cellulose, starch, pyruvate, choline, glutamate, histidine, serine, threonine and casamino acids. End products of metabolism were acetate, butyrate, caproate, ethanol and hexanol. Dominant cellular fatty acids (>10 %) were C_16 : 0 (41.5 %), C_16 : 1 ω7c/C_16 : 1 ω6c (10.0 %), and a summed feature containing cyclo C_17 : 1/C_18 : 0 (17.3 %). Based on the phenotypic, chemotaxonomic, phylogenetic and phylogenomic analyses, strain P21^T represents a new species in the genus Clostridium, for which the name Clostridium muellerianum sp. nov. is proposed. The type strain is P21^T (=DSM 111390^T=NCIMB 15261^T).