Comparative genomics and proposal of Streptomyces radicis sp. nov., an endophytic actinomycete from roots of plants in Thailand*

Strains DS1-2T and AZ1-7, which were isolated from roots of plants, were taxonomically characterized based on polyphasic taxonomic and taxogenomic approaches. Both strains were Gram-stain-positive and filamentous bacteria which contained LL-diaminopimelic acid in cell-wall peptidoglycan and glucose and ribose in whole-cell hydrolysates. MK-9(H6), MK-10(H6), MK-9(H8), MK-10(H8) and MK-10(H4) were major menaquinones; iso-C16:0 and iso-C16:1G were predominant cellular fatty acids; diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol mannoside presented as major phospholipids; and the DNA G+C contents of 73.2 mol%. Strains DS1-2T and AZ1-7 showed 97.6-98.0 % 16S rRNA gene sequence similarity, 81.0-82.0 % ANIb, 84.8-85.3 % ANIm and 22.0-23.1 % digital DDH to their related type strains: S. specialis GW41-1564T and S. hoynatensis S1412T. Comparative genomics results of these strains and their related type strains also revealed the differences and distributions of key genes associated with stress responses, environmental variables, plant interactions and bioactive metabolites. Based on the phenotypic, chemotaxonomic and genomic data, strains DS1-2T and AZ1-7 could be assigned to the novel species within the genus Streptomyces for which the name Streptomyces radicis sp. nov. is proposed. The type strain is DS1-2T (=JCM 32152T =KCTC 39738T =TISTR 2403T).

Automated summary

Strains DS1-2T and AZ1-7, isolated from plant roots, were taxonomically characterized as novel species Streptomyces radicis sp. nov. based on phenotypic, chemotaxonomic and genomic data. The strains showed differences in key genes associated with stress responses, environmental variables, plant interactions and bioactive metabolites compared to their related type strains.