Subtercola boreus gen. nov., sp. nov. and Subtercola frigoramans sp. nov., two new psychrophilic actinobacteria isolated from boreal groundwater

Abstract

Psychrophilic actinobacterial isolates from permanently cold groundwater in Finland were characterized using a polyphasic approach. Growth on agar plates was observed at temperatures down to -2 °C, with an optimum at 15-17 °C, but no growth was observed at 30 °C. The peptidoglycan type was B2γ and the characteristic diamino acid was diaminobutyric acid. The cell wall sugars of strain K265(T) were rhamnose, ribose, xylose and mannose and those of strain K300(T) were glucose, rhamnose and xylose. The polar lipids included phosphatidylglycerol, diphosphatidylglycerol, one unknown phospholipid and two glycolipids. The main whole-cell fatty acids were 12-methyltetradecanoic acid, 14-methylpentadecanoic acid and 14-methylhexadecanoic acid. Large amounts of anteiso-1,1-dimethoxy-pentadecane and also iso-1,1-dimethoxyhexadecane were present as diagnostic markers. The predominant menaquinones were MK-9 and MK-10. The G+C content of the DNA of strains K265(T) and K300(T) was 64.4 and 67.8 mol%, respectively. Comparison of 16S rRNA gene sequences revealed that strains K265(T) and K300(T) represent a new lineage among the type-B-peptidoglycan actinomycetes. The closest relatives were Clavibacter michiganensis, Frigoribacterium faeni and Rathayibacter rathayi. On the basis of 16S rDNA sequence, G+C content and chemotaxonomical and physiological characteristics, K265(T) and K300(T) clearly represent a new genus. The genus Subtercola gen. nov. is described, together with two species, namely Subtercola boreus sp. nov. (type strain K300(T) = DSM 13056(T) = CCUG 43135(T)) and Subtercola frigoramans sp. nov (type strain K265(T) = DSM 13057(T) = CCUG 43136(T)).