Three novel actinomycetes, Nocardia spongicola sp. nov., Pseudonocardia oceanicola sp. nov. and Streptomyces callyspongiae sp. nov., isolated from marine sponges

Marine sponges are important reservoirs of diverse and previously undescribed microorganisms. In this study, four actinomycete strains, 004ᵀ, RS010ᵀ, TR02-1ᵀ, and TR06-5, were isolated from marine sponges collected from Mun Nork and Mun Nai Islands, Rayong Province, Thailand. A polyphasic taxonomic approach, including 16S rRNA gene sequence analysis, phylogenomic analysis, chemotaxonomic characterization, and comparative genomic analysis, was used to determine their taxonomic positions. Strains 004ᵀ, RS010ᵀ, and TR02-1ᵀ represented three distinct species within the genera Nocardia , Pseudonocardia , and Streptomyces , respectively, whereas strain TR06-5 was assigned to the same species as strain TR02-1ᵀ. Comparative genomic analyses based on ANI and dDDH values supported their distinction from the closest related type strains. Genome mining revealed several biosynthetic gene clusters, suggesting the potential of these strains to produce secondary metabolites. Based on these results, three novel species are proposed: Nocardia spongicola sp. nov. (type strain 004ᵀ = TBRC 19730ᵀ = NBRC 117342ᵀ), Pseudonocardia oceanicola sp. nov. (type strain RS010ᵀ = TBRC 19731ᵀ = NBRC 117250ᵀ), and Streptomyces callyspongiae sp. nov. (type strain TR02-1ᵀ = TBRC 19732ᵀ = NBRC 117343ᵀ). Crude secondary metabolite extracts from strains 004ᵀ and RS010ᵀ exhibited cytotoxic activity against H460 human non-small-cell lung cancer cells and induced apoptotic features, including nuclear condensation and DNA fragmentation, without detectable necrotic cell death after 24 h of treatment. These findings further support the potential of Nocardia spongicola 004ᵀ and Pseudonocardia oceanicola RS010ᵀ as promising sources of bioactive compounds with anticancer activities.