Streptomyces mahasarakhamensis sp. nov., an Endophytic Actinobacterium Isolated from Jasmine Rice and its Potential as plant Growth Promoter

Two endophytic actinobacteria, strains MK5^T and MK7, were isolated from the surface-sterilized root of Jasmine rice (Oryza sativa KDML 105). These strains were aerobic actinobacteria with a well-developed substrate and aerial mycelia that formed spiral spore chains. The type strains that shared the high 16S rRNA gene sequence similarity with both strains were Streptomyces naganishii NBRC 12892^T (99.4%), “Streptomyces griseicoloratus” TRM S81-3^T (99.2%), and Streptomyces spiralis NBRC 14215^T (98.9%). Strains MK5^T and MK7 are the same species sharing a digital DNA–DNA hybridization (dDDH) value of 95.3% and a 16S rRNA gene sequence similarity of 100%. Chemotaxonomic data confirmed the affiliation of strains MK5^T and MK7 to the genus Streptomyces. Strains MK5^T and MK7 contained MK-9(H₄) as a major menaquinone; the whole-cell sugar of both strains was galactose and glucose. The strain MK5^T shared 93.4% average nucleotide identity (ANI)-Blast, 95.5% ANI-MUMmer, 93% average amino acid identity, and 61.3% dDDH with S. spiralis NBRC 14215^T. The polyphasic approach confirmed that strain MK5^T represents a novel species, and the name Streptomyces mahasarakhamensis sp. nov. is proposed. The type strain is MK5^T (= TBRC 17754 = NRRL B-65683). Genome mining, using an in silico approach and searching biosynthesis gene clusters of strains MK5^T and MK7, revealed that the genomes contained genes encoding proteins relating to plant growth promotion, bioactive compounds, and beneficial enzymes. Strains MK5^T and MK7 could produce indole acetic acid and solubilize phosphate in vitro.