Streptomyces xanthii sp. nov. and Streptomyces roseirectus sp. nov. isolated from a Chinese medicinal plant

Two strains of Actinobacteria, designated CRXT-Y-14(T) and CRXT-G-22(T) , were isolated from the healthy leaves and seeds, respectively, of a medicinal plant Xanthium sibiricum. Their taxonomic positions were determined using a polyphasic approach. Strain CRXT-Y-14(T) produced flexuous chains of smooth-surfaced spores. Strain CRXT-G-22(T) produced straight chains of smooth surfaced spores. Their morphological features were consistent with the diagnostic characteristics of members of the genus Streptomyces. The results of 16S rRNA gene sequence analyses indicated two strains represented members of the genus Streptomyces. CRXT-Y-14(T) shared 99.3, 98.9, 98.8 % sequence similarities to Streptomyces atriruber NRRL B-24165(T) , Streptomyces avermitilis MA-4680(T) and Streptomyces davaonensis JCM 4913(T) , respectively. Whilst CRXT-G-22(T) exhibited highest similarity to Streptomyces acidiscabies ATCC 49003(T) (98.9 %). The results of phylogenetic analyses based on 16S rRNA gene sequences indicated that the closest phylogenetic neighbours of strains CRXT-Y-14(T) and CRXT-G-22(T) were S. atriruber NRRL B-24165(T) and S. acidiscabies ATCC 49003(T) , respectively. The phylogenomic analyses further confirmed the relative relationship between strain CRXT-G-22(T) and S. acidiscabies ATCC 49003(T) , but indicated that CRXT-Y-14(T) could represent a novel species of the genus Streptomyce. However, the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between CRXT-Y-14(T) and strain CRXT-G-22(T) , between CRXT-Y-14(T) and S. atriruber NRRL B-24165(T) , and between CRXT-G-22(T) and S. acidiscabies ATCC 49003(T) were 85.4 and 23.2 %, 85.8 and 23.9 % and 89.1 and 34.1 %, respectively, far below the 95-96 and 70 % cut off points recommended for delineating species. Furthermore, these two novel isolates were distinctly differentiated from their relatives in the genus Streptomyces with respect to phenotypic and chemotaxonomic characteristics. On the basis of these data, CRXT-Y-14(T) and CRXT-G-22(T) clearly represent two novel species within the genus Streptomyces , for which the names Streptomyces xanthii sp. nov. (type strain CRXT-Y-14(T) = MCCC 1K04966(T)=JCM 34527(T)) and Streptomyces roseirectus sp. nov. (type CRXT-G-22(T) = MCCC 1K04979(T)=JCM 34565(T)) are proposed.