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 7R015^T and 7R016^T, 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-C_{16 : 0} and anteiso-C_{15 : 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 7R015^T showed the highest similarity to that of Streptomyces pseudovenezuelae DSM 40212^T (98.6 %), Streptomyces cyaneus NRRL B2296^T (98.6 %) and Streptomyces curacoi DSM 40107^T (98.6 %). Strain 7R016^T showed the highest 16S rRNA gene sequence similarity to Streptomyces gilvifuscus NBRC 110904^T (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 7R015^T, 7R016^T 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 7R015^T and 7R016^T represent novel species of the genus Streptomyces and are named herein as Streptomyces cylindrosporus sp. nov. (=NBRC 115200^T = TBRC 14542^T) for strain 7R015^T and Streptomyces spinosisporus sp. nov. (=NBRC 115201^T = TBRC 14543^T) for strain 7R016^T.

Keywords: Acanthaceae; Barleria lupulina; Streptomyces; endophyte; novel actinobacteria.