Endophytic actinobacterial strain 3R004T was isolated from a root of Justicia subcoriacea collected in Thailand. In this report, the taxonomic position of this strain is described using a polyphasic approach. Based on the morphological characteristics and chemical composition of its cells, strain 3R004T was identified as a member of the genus Streptomyces. It produced a long chain of cylindrical spores on aerial mycelia. ll-Diaminopimelic acid was detected in the cell wall peptidoglycan. The menaquinones were MK-9(H4), MK-9(H6) and MK-9(H8). C16 : 0, iso-C16 : 0, anteiso-C15 : 0 and iso-C15 : 0 were detected as the major cellular fatty acids. Polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and one unidentified lipid. Strain 3R004T showed the highest 16S rRNA gene similarity of 99.45 % to Streptomyces cyaneochromogenes MK-45T. The phylogenomic results indicated that strain 3R004T was close to Streptomyces aquilus GGCR-6T and Streptomyces antibioticus DSM 40234T. The DNA-DNA hybridization and average nucleotide identity values among strain 3R004T and closely related Streptomyces species were 35.5-63.1 % and 82.7-94.3 %, respectively. The type strain produced actinomycin D antibiotic as the major secondary metabolite. The maximum productivity of the actinomycin D (378 mg l-1) was observed when the strain was grown in 301 broth at 30 °C, 180 r.p.m. for 12 days. On the basis of phenotypic and genotypic evidence, strain 3R004T represents a novel species of the genus Streptomyces, for which the name Streptomyces justiciae is proposed. The type strain is 3R004T (=LMG 32138T=TBRC 13128T=NBRC 115065T).
Keywords: Acanthaceae; actinomycin D; antibiotics; endophyte; novel streptomyces.