Ecological distribution and secondary metabolites of marine actinobacteria: a comprehensive review

Actinobacteria are a diverse group of Gram-positive bacteria characterized by high guaninecytosine (G+C) content and broad ecological distribution across terrestrial, marine, and extreme environments. Marine-derived and extremophilic actinobacteria have attracted significant scientific interest due to their ability to produce structurally diverse secondary metabolites and industrially important enzymes. This review highlights the ecology, taxonomy, morphology, and metabolic diversity of actinobacteria, with special emphasis on marine and extremophilic species. Their complex morphological structures, including filamentous mycelia and spore-forming capabilities, play an essential role in identification and adaptation to diverse habitats. The review further discusses the biosynthetic potential of actinobacteria, particularly the polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) pathways, which produce valuable bioactive compounds such as abyssomicin C and salinosporamide A, which exhibit antimicrobial, anticancer, and pharmaceutical significance. Additionally, extremophilic actinobacteria produce unique extremozymes that are remarkably stable under harsh environmental conditions, making them suitable for industrial and biotechnological applications. Despite their immense potential, challenges such as slow growth rates, low biomass yield, and difficulties in cultivation hinder large-scale production and enzyme recovery. Advanced approaches, including metagenomics, genome mining, and heterologous expression, have emerged as promising strategies for accessing uncultivable strains and cryptic biosynthetic gene clusters. Overall, marine and extremophilic actinobacteria represent an important resource for novel drug discovery, environmental sustainability, and future biotechnological innovation.