Exploring the antimicrobial potential of marine actinobacteria from the Fijian hard corals

Abstract

Marine ecosystems, particularly corals and their microbiomes, are recognized as prolific sources of unique natural products with diverse bioactivities. Despite the evident paucity of literature on microbial compounds associated with Fijian corals, this study aims to explore and elucidate the potential of actinomycetes associated with Fijian hard corals as sources of bioactive compounds. To highlight, actinomycete strains were isolated from five hard coral genera using three distinct isolation media. Among these, all 41 strains are facultative salt-tolerant, with 16 demonstrating biological activity by inhibiting the growth of three or more test pathogen strains. Interestingly, all ethyl acetate extracts of putative strains exhibited varying degrees of antimicrobial activity, with isolates FJC 16, 28, 33, and 41 being the most active. Moreover, the brine shrimp lethality test confirmed that actinomycete strain FJC 16 exhibited the highest toxicity toward brine shrimps with a lethal concentration of 37.50 μg/mL for 50% of the test population. The International Streptomyces Project medium-2 demonstrated high efficiency in isolating total actinomycetes. With a focus on cultivation techniques, the applications of pretreatment practices contributed to a successive recovery of actinomycetes. The current study serves as a foundational effort to evaluate the biosynthetic capabilities of Fijian hard corals, aiming to advance the current frontier of microbial natural product research within coral-associated microbiomes. Overall, as the footprint of microbial metabolites grows, Fijian hard corals represent a valuable prospect for further advanced studies of microbial designer molecules or analogs.

Keywords

Actinobacteria / Bioactive molecules / Microbial activity / Corals / Bioactive screening / Fiji

Acknowledgments

The authors thank the University of the South Pacific (Research Office and School of Agriculture, Geography, Environment, Ocean, and Natural Sciences) for the facilities provided. This acknowledgement is extended to the Fiji Government through its Ministry of Education and Fisheries for permission to conduct the research in Fiji.

Funding

The University of the South Pacific provided research funding support to the lead author, GS, for culture-based studies (grand no.: FD024 FST12 71502 001).

Conflict of interest

The authors declared no conflict of interest.

Author contributions

Conceptualization: Galana Siro, Ketan Christi

Funding acquisition: Galana Siro

Investigation: Galana Siro

Methodology: Galana Siro

Supervision: Ketan Christi, Tamara Osborne

Writing-original draft: Galana Siro

Writing-review & editing: All authors

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Availability of data

The data generated and analyzed are included in this manuscript.

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