Streptomyces sediminimaris sp. nov., a novel actinobacterium with anticancer potential isolated from mangrove sediments

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Two marine actinomycete-like strains, MCC20 T and MCC57, were isolated from Chanthaburi (Thailand) mangrove sediment. Their taxonomic classifications were established through a polyphasic approach. Despite differences in colony morphotypes, genetic and chemotaxonomic analyses confirmed them as the same species within the genus Streptomyces . Both strains contained ll -diaminopimelic acid in their cell wall, with glucose, mannose, ribose and rhamnose identified as whole-cell sugars. Their phospholipid profile comprises phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and phosphatidylinositol mannoside. The predominant fatty acids were iso-C 15:0 , anteiso-C 15:0 , iso-C 16:0 and anteiso-C 17:0 with MK-9(H 8 ) as the primary menaquinone, while MK-9(H 6 ) and MK-9(H 4 ) were unique to strain MCC57. Both strains exhibited anticancer activity against colorectal (HCT116) and lung (A549) cancer cells, with strain MCC20 T being more potent. Their 16S rRNA gene sequences showed 100% similarity, with 99.2% similarity to Streptomyces fumigatiscleroticus NBRC 12999 T . Nevertheless, a phylogenomic tree placed them closer to Streptomyces spinosirectus CRSS-Y-16 T , Streptomyces plumbidurans KC 17012 T and Streptomyces spinosisporus 7R016 T . Nearly 100% average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values highlighted the identity of strains MCC20 T and MCC57, while ANI (89.4%) and dDDH (35.5%) values were well below the respective 95 and 70% thresholds for related species. This supported their novelty. Based on their genotypes and phenotypes, strains MCC20 T (=NBRC 117131 T =TBRC 19240 T ) and MCC57 (=NBRC 117132=TBRC 19241) are identified as phenotypic variants of a new species, Streptomyces sediminimaris sp. nov., with strain MCC20 T designated as the type strain (~9.2 Mb genome, 72.0 mol% G+C content).