The taxonomic position of a novel aerobic, Grampositive actinobacteria, designated strain RB5(T), was determined using a poly phasic approach. The strain, isolated from the gut of the fungusfarming termite Macrotermes natalensis, showed morphological, physiological and chemotaxonomic properties typical of the genus Streptomyces. Based on 16S rRNA gene sequence analysis, the closest phylogenetic neighbour of RB5(T) was Streptomyces polyrhachis DSM 42102(T) (98.87 %). DNA-DNA hybridization experiments between strain RB5(T) and S. polyrhachis DSM 42102(T) resulted in a value of 27.4 % (26.8 %). The cell wall of strain RB5(T) contained iota iota diaminopimelic acid as the diagnostic amino acid. Mycolic acids and diagnostic sugars in whole cell hydrolysates were not detected. The strain produced the following major phospholipids: diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannoside and phosphatidylserine. The menaquinone profile showed hexaand octahydrogenated menaquinones containing nine isoprene units [MK-9(H-6) and MK-9(H-8)]. The strain exhibited a fatty acid profile containing the following major fatty acids: 12methyltridecanoic acid (isoC(14:0)) 12-methyltetradecanoic acid (anteiso-C-15:0), 13-methyltetradecanoic acid (isoC(15:0)) and 14-methylpentadecanoic acid (isoC(16:0)). ... mehrHere, we propose a novel species of the genus Streptomyces - Streptomyces smaragdinus with the type strain RB5(T) (=VKM Ac-2839(T)=NRRL B65539(T)).