Streptomyces caeruleatus sp. nov., with dark blue diffusible pigment.

An actinomycete, designated strain GIMN4.002(T), was isolated from a tomato rhizosphere soil sample in Guangzhou, China. The strain produces white aerial mycelium and dark blue diffusible pigment on Gause's synthetic agar, and microscopic observation revealed that it produces looped chains of spiny spores. Morphological and chemotaxonomic characteristics of the strain are typical of the genus Streptomyces. Melanin was produced and antibacterial activity was detected against Gram-positive micro-organisms, such as Bacillus subtilis, Micrococcus luteus and Staphylococcus aureus. The 16S rRNA gene sequence of strain GIMN4.002(T) had highest similarity (99.4  %) to Streptomyces lincolnensis B91; however, DNA-DNA relatedness between strain GIMN4.002(T) and S. lincolnensis NBRC 13054(T) was only 32.17  %. Further, the morphological, physiological and biochemical characteristics of strain GIMN4.002(T) are distinct from S. lincolnensis and other species of the genus Streptomyces with which this strain has high 16S rRNA gene sequence similarity (98-99  %). On the basis of the physiological and molecular properties observed, it is proposed that strain GIMN4.002(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces caeruleatus sp. nov. is proposed, with GIMN4.002(T) (=CCTCC M 208213(T) =NRRL B-24802(T)) as the type strain.