Potential antibiotic production of Streptomyces justiciae sp. nov., isolated from the root of Justicia subcoriacea

Endophytic actinobacterial strain 3R004T was isolated from a root of Justicia subcoriacea collected in Thailand. In this report, the taxo-nomic position of this strain is described using a polyphasic approach. Based on the morphological characteristics and chemical com-position of its cells, strain 3R004(T) 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(H-4), MK-9(H-6) and MK-9(H-8). C-16:0, iso-C-16:0, anteiso-C-15: 0 and iso- C-15: 0 were detected as the major cellular fatty acids. Polar lipids were diphosphatidyl-glycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and one unidentified lipid. Strain 3R004(T) showed the highest 16S rRNA gene similarity of 99.45 % to Streptomyces cyaneochromogenes MK-45(T). The phylogenomic results indicated that strain 3R004(T) was close to Streptomyces aquilus GGCR-6(T) and Streptomyces antibioticus DSM 40234(T). The DNA-DNA hybridization and average nucleotide identity values among strain 3R004(T) 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 degrees C, 180 r.p.m. for 12 days. On the basis of phe-notypic and genotypic evidence, strain 3R004(T) represents a novel species of the genus Streptomyces, for which the name Streptomyces justiciae is proposed. The type strain is 3R004T (=LMG 32138(T)=TBRC 13128(T)=NBRC 115065(T)).

Automated summary

In this study, endophytic actinobacterial strain 3R004T was isolated from the root of Justicia subcoriacea collected in Thailand. Through a polyphasic approach, it was identified as a member of the genus Streptomyces, producing actinomycin D as a major secondary metabolite. The taxonomic position and characteristics of strain 3R004(T) were determined using morphological, chemical, and phylogenomic analyses.