Caenibacterium thermophilum gen. nov., sp nov., isolated from a thermophilic aerobic digester of municipal sludge

A bacterial strain, N2-680T (=DSM 15264T=LMG 21760T), isolated from a thermophilic aerobic digester of municipal sludge, was characterized with respect to its morphology, physiology and taxonomy. Phenotypically, the isolate was a Gram-negative rod with a polar flagellum, catalase- and oxidase-positive, containing cytoplasmic inclusions of poly-β-hydroxybutyrate and had an optimal growth temperature of about 47 °C. Strain N2-680T was unable to reduce nitrate and could use organic acids, amino acids and carbohydrates as single carbon sources. Chemotaxonomic analysis revealed that ubiquinone 8 was the major respiratory quinone of this organism and that phosphatidylethanolamine and phosphatidylglycerol were the major polar lipids. At 50 °C, the major components in fatty acid methyl ester analysis were C16 : 0 and cyclo-C17 : 0. The highest 16S rDNA sequence identity of isolate N2-680T was to Leptothrix mobilis and Ideonella dechloratans (95·7 %) and to Rubrivivax gelatinosus and Aquabacterium commune (95·6 %). 16S rDNA sequence similarities to species of two related thermophilic genera, Caldimonas manganoxidans and Tepidimonas ignava, were lower (93·6 and 94·7 %). On the basis of phylogenetic analyses and physiological and chemotaxonomic characteristics, it is proposed that isolate N2-680T represents a new genus and species, for which the name Caenibacterium thermophilum gen. nov., sp. nov. is proposed.