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

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 <i>Streptomyces</i>. 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(H₈) as the primary menaquinone, while MK-9(H₆) and MK-9(H₄) 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 <i>Streptomyces fumigatiscleroticus</i> NBRC 12999^T. Nevertheless, a phylogenomic tree placed them closer to <i>Streptomyces spinosirectus</i> CRSS-Y-16^T, <i>Streptomyces plumbidurans</i> KC 17012^T and <i>Streptomyces spinosisporus</i> 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, <i>Streptomyces sediminimaris</i> sp. nov., with strain MCC20^T designated as the type strain (~9.2 Mb genome, 72.0 mol% G+C content).