Streptomyces cylindrosporus sp. nov. and Streptomyces spinosisporus sp. nov.: two new endophytic actinobacteria isolated from the roots of Barleria lupulina Lindl.

Abstract

Two endophytic actinobacteria, designated as strains 7R015T and 7R016T, were isolated from the roots of Barleria lupulina collected in Thailand. The morphological characteristics and results of chemotaxonomic studies and 16S rRNA gene analysis indicated that both strains represented members of the genus Streptomyces . They contained ll-diaminopimelic acid in the peptidoglycan. Ribose and glucose were detected as the whole-cell sugars. MK-9(H4), MK-9(H6) and MK-9(H8), were found as the membrane menaquinone. The predominant cellular fatty acids detected were iso-C16 : 0 and anteiso-C15 : 0. The genomes of both strains harboured biosynthetic gene clusters for melanin, terpene, lanthipeptide, polyketides, non-ribosomal peptide synthetase, siderophore and ectoine. The 16S rRNA gene sequence of 7R015T showed the highest similarity to that of Streptomyces pseudovenezuelae DSM 40212T (98.6 %), Streptomyces cyaneus NRRL B2296T (98.6 %) and Streptomyces curacoi DSM 40107T (98.6 %). Strain 7R016T showed the highest 16S rRNA gene sequence similarity to Streptomyces gilvifuscus NBRC 110904T (98.2 %), which is lower than the threshold value for 16S rRNA gene sequence similarity for differentiation at the species level (98.65 %). Comparative genome analysis revealed that the genomes of 7R015T, 7R016T and the closely related type strains had an average nucleotide identity (ANI) of less than 95 % and a digital DNA–DNA hybridisation (dDDH) of less than 70 %, the thresholds for species demarcation. On the basis of the results of the polyphasic study, strains 7R015T and 7R016T represent novel species of the genus Streptomyces and are named herein as Streptomyces cylindrosporus sp. nov. (=NBRC 115200T = TBRC 14542T) for strain 7R015T and Streptomyces spinosisporus sp. nov. (=NBRC 115201T = TBRC 14543T) for strain 7R016T.