Emthomya N.Chuangrattanawan C.Ngamcharungchit C.Kongsaya T.Kanchanasin P.Phongsopitanun W.Suriyachadkun C.Pidot S.J.Intra B.Mahidol University2025-06-302025-06-302025-01-01International Journal of Systematic and Evolutionary Microbiology Vol.75 No.6 (2025)14665026https://repository.li.mahidol.ac.th/handle/123456789/110999Two 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<inf>15:0</inf>, anteiso-C<inf>15:0</inf>, iso-C<inf>16:0</inf> and anteiso-C<inf>17:0</inf> with MK-9(H<inf>8</inf>) as the primary menaquinone, while MK-9(H<inf>6</inf>) and MK-9(H<inf>4</inf>) 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).Agricultural and Biological SciencesImmunology and MicrobiologyArticleSCOPUS10.1099/ijsem.0.0068112-s2.0-1050087057801466503440512541