Rectinema cohabitans gen. nov., sp nov., a rod-shaped spirochaete isolated from an anaerobic naphthalene-degrading enrichment culture

The anaerobic, non-motile strain HMT was isolated from the naphthalene-degrading, sulfate-reducing enrichment culture N47. For 20 years, strain HMT has been a stable member of culture N47 although it is neither able to degrade naphthalene nor able to reduce sulfate in pure culture. The highest similarity of the 16S rRNA gene sequence of strain HMT ( 89 %) is with a cultivated member of the family Spirochaetaceae, Treponema caldarium strain H1(T) (= DSM 7334(T)), an obligately anaerobic, thermophilic spirochaete isolated from cyanobacterial mat samples collected at a freshwater hot spring in Oregon, USA. In contrast to this strain and the majority of spirochaete species described, strain HMT showed a rod-shaped morphology. Growth occurred at temperatures between 12 and 50 degrees C ( optimum 37 degrees C) but the isolate was not able to grow at 60 ffi C. The strain fermented various sugars including D-glucose, D-fructose, lactose and sucrose. Addition of 0.1% ( w/v) yeast extract or 0.1% ( w/v) tryptone to the culture medium was essential for growth and could not be replaced by either the vitamin solutions tested or by 0.1% ( w/v) peptone or 0.1% ( w/v) casamino acids. The DNA G+C content of the isolate was 51.5 mol%. The major fatty acids were C-14 : 0, C-18 : 1 omega(13)c, C-16 : 1 omega 9t, C-16 : 1 omega 11c and C-16 : 1 omega 9c. Based on the unique morphology and the phylogenetic distance from the closest cultivated relative, a novel genus and species, Rectinema cohabitans gen. nov., sp. nov., is proposed. The type strain is strain HMT (= DSM 100378(T)= JCM 30982(T)).