Clostridium clariflavum sp. nov. and Clostridium caenicola sp. nov., moderately thermophilic, cellulose-/cellobiose-digesting bacteria isolated from methanogenic sludge

Abstract

Two novel anaerobic, moderately thermophilic and cellulose-/cellobiose-digesting bacteria, EBR45(T) and EBR596(T), were isolated from anaerobic sludge of a cellulose-degrading methanogenic bioreactor. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains belonged to cluster III within the low-G+C-content Gram-positive bacteria. The close relatives of EBR45(T) were Clostridium straminisolvens DSM 16021(T) (sequence identity, 94.6 %) and Clostridium thermocellum DSM 1237(T) (93.4 %). The closest relative of EBR596(T) was Clostridium stercorarium DSM 8532(T) (95.9 %). Both isolates were rod-shaped sporulators, growing optimally at 60 degrees C. EBR45(T) was Gram-staining-reaction-variable and non-motile, formed bright-yellow colonies on solid media, and grew on a relatively narrow range of carbohydrates including cellulose and cellobiose. EBR596(T) was Gram-staining-reaction-negative and motile, formed glossy white colonies and grew on cellobiose and various carbohydrates except cellulose. Major fatty acid compositions were 16 : 0 iso, 16 : 0 and 16 : 0 dimethylacetal (strain EBR45(T)) and 15 : 0 iso, 16 : 0 iso, 15 : 0 anteiso and 17 : 0 anteiso (strain EBR596(T)). The DNA G+C contents were 36.9 mol% (EBR45(T)) and 51.1 mol% (EBR596(T)). Based on the phenotypic and phylogenetic data and genomic distinctiveness, strains EBR45(T) and EBR596(T) represent two novel species, for which the names Clostridium clariflavum sp. nov. (type strain EBR45(T) =DSM 19732(T) =NBRC 101661(T)) and Clostridium caenicola sp. nov. (type strain EBR596(T) =DSM 19027(T) =NBRC 102590(T)) are proposed.