A novel actinomycete, strain RY43- 2T, belonging to the genus Streptomyces, was isolated from a peat swamp forest soil col-lected from Rayong Province, Thailand. The strain was characterized by using a polyphasic approach. The cell -wall pepti-doglycan contained LL-diaminopimelic. Ribose and glucose were detected in its whole -cell hydrolysates. The strain contained anteiso-C15:0, iso-C14:0 and iso-C16:0 as the predominant fatty acids, and MK-9(H4), MK-9(H6) and MK -9(H8) as the major menaqui-nones. The phospholipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinosi-tol, phosphatidylinositol mannoside, three unidentified ninhydrin-positive phospholipids and two unidentified phospholipids. Strain RY43-2T showed the highest 16S rRNA gene similarity to Streptomyces misionensis JCM 4497T (98.9 %) and Streptomyces lichenis LCR6-01T (98.9 %). The draft genome of RY43- 2T was 6.7 Mb with 6078 coding sequences with an average G+C content of 70.8 mol%. Genomic analysis revealed that the average nucleotide identity (ANI) values based on BLAST (ANIb) and MUMmer (ANIm) between strain RY43- 2T and S. misionensis JCM 4497T were 80.1 and 86.1%, respectively. The ANIb and ANIm values between strain RY43- 2T and S. lichenis LCR6-01T were 77.0 and 85.5%, respectively. The digital DNA-DNA hybridization values were 25.2 and 23.0% in comparison with the draft genomes of S. misionensis JCM 4497T and S. lichenis LCR6-01T, respectively. The results of taxonomic analysis suggested that strain RY43- 2T represented a novel species of the genus Streptomyces for which the name Streptomyces macrolidinus sp. nov. is proposed. The type strain is RY43- 2T (=TBRC 7286T=NBRC 115640T). Strain RY43-2T exhibited antimicrobial activity against Enterococcus faecium ATCC 51559, Colletotrichum capsici BMGC 106 and Colletotrichum gloeosporioides BMGC 107 with the minimum inhibitory concentration values of 25.0, 12.5, and 6.25 mu g ml-1. It also exhibited potent antimalarial activity against Plasmodium falciparum K1 with IC50 of 0.0031 mu g ml-1. In addition, it showed cytotoxicity against Vero, KB, MCF- 7 and NCI -H187 with IC50 values of 0.0347, 6.15, 3.36 and 0.0352 mu g ml-1, respectively.
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