Clostridium gelidum sp. nov., a psychrotrophic anaerobic bacterium isolated from rice field soil

A cold-adapted or psychrotrophic anaerobic bacterial strain (C5S11 T ) was isolated from rice field soil in Japan using an enrichment culture incubated at 5 °C. C5S11 T grew at 0 °C and optimum growth was observed at 10 °C. Cells of C5S11 T were Gram-stain-positive, motile, spore-forming rods with peritrichous flagella. C5S11 T was assigned to a large branch consisted of various mesophilic species of the genus Clostridium in the phylogenetic trees reconstructed using the 16S rRNA gene sequences. The most closely related species of the strain was Clostridium chromiireducens DSM 23318 T (98.5 % sequence similarity). C5S11 T fermented various carbohydrates, including polysaccharides (starch, inulin, pectin and xylan), and produced acetate, butyrate and H 2 as major products. The major cellular fatty acids were C 16 : 0 , C 16 : 1 ω9 c , C 14 : 0 and C 16 : 1 ω7 c . The diagnostic diamino acid of the cell wall peptidoglycan was meso -diaminopimelic acid. The genome size of C5S11 T was 6.04 Mb and the genomic DNA G+C content was 29.0 mol%. Average nucleotide identity by blast (ANIb), avaerage amino acid identity (AAI) and digital DNA–DNA hybridization (dDDH) values between the genomes of C5S11 T and C. chromiireducens DSM 23318 T were 80.0, 75.2 and 26.4 %, respectively. C5S11 T had a gene encoding cold shock protein (RNA chaperone) in the genome, homologues of which have been found in psychrophilic species of the genus Clostridium . On the basis of the differences in the phylogenetic, genomic and phenotypic characteristics of C5S11 T from those of the closely related species, a novel species, Clostridium gelidum sp. nov., is proposed to accommodate the strain. The type strain is C5S11 T (=NBRC 114689 T = DSM 112608 T ).