Microbial secondary metabolites are an important source of antibiotics currently available for combating drug-resistant pathogens. These important secondary metabolites are produced by various microorganisms, including Actinobacteria. Actinobacteria have a colossal genome with a wide array of genes that code for several bioactive metabolites and enzymes. Numerous studies have reported the isolation and screening of millions of strains of actinomycetes from various habitats for specialized metabolites worldwide. Looking at the extent of the importance of actinomycetes in various fields, corals are highlighted as a potential hotspot for untapped secondary metabolites and new bioactive metabolites. Unfortunately, knowledge about the diversity, distribution and biochemistry of marine actinomycetes compared to hard corals is limited. In this review, we aim to summarize the recent knowledge on the isolation, diversity, distribution and discovery of natural compounds from marine actinomycetes associated with hard corals. A total of 11 new species of actinomycetes, representing nine different families of actinomycetes, were recovered from hard corals during the period from 2007 to 2022. In addition, this study examined a total of 13 new compounds produced by five genera of actinomycetes reported from 2017 to 2022 with antibacterial, antifungal and cytotoxic activities. Coral-derived actinomycetes have different mechanisms of action against their competitors.

The South Pacific Journal of Natural Science (SPJNS) is published online by CSIRO PUBLISHING on behalf of the Faculty of Science and Technology, The University of the South Pacific, Fiji. The normal focus of the journal is to disseminate scientific research work carried out in the Pacific.

Actinobacteria produce a plethora of bioactive molecules, yet research on these bacteria in the Pacific Island nations remains scarce. Previously, we isolated 16 actinomycete strains from Fijian hard corals, with varying degrees of antimicrobial activity against common pathogenic strains. The present study aims to identify these bioactive actinomycete isolates using 16S ribosomal RNA (16S rRNA) gene sequencing and phylogenetic analysis. The 16S rRNA gene characterization of the bioactive isolates predominantly revealed members of the genus Streptomyces, alongside three rare actinomycete genera: Micromonospora, Prauserella, and Kocuria. Additionally, antiSMASH analysis of the closest phylogenetic relatives of these cultured actinobacteria with notable antimicrobial activity revealed a strong potential for antibiotic biosynthesis. Overall, these findings suggest that Fijian hard corals represent a promising reservoir of bioactive actinobacteria for the discovery of antimicrobial compounds, particularly Streptomyces spp.