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.

Bioprospecting of novel antibiotics has been the conventional norm of research fostered by researchers worldwide to combat drug resistance. With the exhaustion of incessant leads, the search for new chemical entities moves into uncharted territories such as the deep sea. The deep sea is a furthermost ecosystem with much untapped biodiversity thriving under extreme conditions. Accordingly, it also encompasses a vast pool of ancient natural products. Actinobacteria are frequently regarded as the bacteria of research interest due to their inherent antibiotic-producing capabilities. These interesting groups of bacteria occupy diverse ecological habitats including a multitude of different deep-sea habitats. In this review, we provide a recent update on the novel species and compounds of actinomycetes from the deep-sea environments within a period of 2016–2022. Within this period, a total of 24 new species of actinomycetes were discovered and characterized as well as 101 new compounds of various biological activities. The microbial communities of various deep-sea ecosystems are the emerging frontiers of bioprospecting.

The search for novel therapeutic agents to combat the crisis of antimicrobial resistance has spanned from terrestrial to unique, marine environments. Currently, most of the drugs available for usage are derived from microbial metabolites, especially those belonging to the bacterial group, actinobacteria. Actinobacteria are hotspot organisms that exist in all habitats with a myriad of unique biosynthetic metabolites. Seagrasses appear to be a key ecosystem within the coastal environment worth bioprospecting for novel natural products. Unfortunately, literature about the bioactive potential of their associated prokaryotes, including actinobacteria remains limited. In this context, this review focused on actinobacteria with antibiotic-producing capabilities derived from different parts of seagrass plants (i.e. roots, rhizomes, and leaves). To date, there were no purified molecules derived from seagrass-associated actinobacteria that were subjected to structure elucidation. From the underpinning of numerous biological profiles such as antibacterial, antifungal, and algicidal activities of seagrass-derived actinobacteria reported in this review during the period from 2012–2020, it provides a continual growth of knowledge accruing overtime, providing a foundation for future research.

Crown of thorns starfish (Acanthaster planci) are coral predators with advantages of having toxicity in their venom and tissue regeneration capabilities. With all these characteristics, only a handful of studies have highlighted the association of microorganisms with this organism. Crown of thorns starfish are common in Fiji and their analyses of microbial diversity for secondary metabolites could be of great interest to the scientific community. This study is an attempt to investigate Fijian-based A. planci for their venom and associated actinomycetes antibacterial activity and further identify the type of enzymes present in the crude venom extract. The CoTS venom extract (0.192 g) harbor enzymes such as gelatinase, caesinase, and amylase. An abundant and potent actinomycete strain, represented as FJA1 showed antibacterial activity against Enterococcus faecium with an inhibition zone of 10 mm. Moreover, all pathogenic test microorganisms were resistant against concentrations of 500 µg and 1 mg of A. planci venom extract.

The cold environments serve as life-entrapping reservoirs of diverse life forms, ranging from eukaryotes to diverse microbial inoculi. Actinobacteria are omnipresent in cold environments, and their existence is notably linked to a remarkable potential for producing and harboring unique metabolites. Their ability to survive in such extreme conditions is supported by a range of adaptations tailored to their specific niche, including cold-resistant traits. In this review, we summarize recent advances (2017–2025) regarding psychrophilic actinobacteria, focusing on newly identified species and novel compounds reported in the literature. Notably, we highlight the discovery of 44 new species as well as nine new compounds across various actinobacteria genera. The inventory of abiotic hurdles associated with cold environments positions this field as a potential hotspot and emerging frontier for sourcing pharmaceutical-like compounds of exceptional ingenuity and complexity. By providing an overview of the recent discoveries in psychrophilic actinobacteria and their intriguing metabolites, this review aims to offer valuable insights to facilitate bioprospecting efforts in cold ecosystems.

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.