Even though soft corals are an integral part of the coral reef ecosystem, very little research has focused on theirendosymbiotic association with the zooxanthellae (Symbiodiniaceae). Symbiotic algae appear in soft corals from both the tropical seas as well as temperate regions across the world. The present study provides a list of soft corals along with their associated zooxanthellae using published data. By combining all the data, 52 soft coral species belonging to 21 genera were identified and their corresponding specific Symbiodiniaceae genera were analysed. It was important to initially compare soft corals and distinguish zooxanthellae at clade level to find any host specificity. The vast majority (75 %) of soft corals predominantly hosted the genus Cladocopium (Clade C) and therefore the focus of this study was to evaluate its geographical distribution. The genus Cladocopium consists of many species which are classified as subclades in this study, exhibiting high intra-clade diversity. For 40 of the 52 soft corals reviewed, 18 % had the same clade type C1 (considered as generalists and ancestral) and 13 % contained the clades C15, C64 and C1:3a, respectively. Analysis showed that some clades (C71a, C15b and C64) were confined to specific geographical regions while clade C1 was distributed worldwide. Understanding the distribution of endosymbionts may enable predictions of which symbioses will survive and exist under future climate change scenarios.

Soft corals, recognized as sessile marine invertebrates, rely mainly on chemical, rather than physical defense, by secreting intricate secondary metabolites with plausible pharmaceutical implication. Their ecological niche encompasses a diverse community of symbiotic microorganisms which potentially contribute to the biosynthesis of these bioactive metabolites. The emergence of new viruses and heightened viral resistance underscores the urgency to explore novel pharmacological reservoirs. Thus, marine organisms, notably soft corals and their symbionts, have drawn substantial attention. In this study, the chemical composition of four Mauritian soft corals: Sinularia polydactya, Cespitularia simplex, Lobophytum patulum, and Lobophytum crassum was investigated using LC–MS techniques. Concurrently, Illumina 16S metagenomic sequencing was used to identify the associated bacterial communities in the named soft corals. The presence of unique biologically important compounds and vast microbial communities found therein was further followed up to assess their antiviral effects against SARS-CoV-2 and HPV pseudovirus infection. Strikingly, among the studied soft corals, L. patulum displayed an expansive repertoire of unique metabolites alongside a heightened bacterial consort. Moreover, L. patulum extracts exerted some promising antiviral activity against SARS-CoV-2 and HPV pseudovirus infection, and our findings suggest that L. patulum may have the potential to serve as a therapeutic agent in the prevention of infectious diseases, thereby warranting further investigation.

Jahajeeah D, Bhoyroo V, Ranghoo-Sanmukhiya M. 2023. Antimicrobial properties and metabolite profiling of the ethyl acetate fractions of Sinularia polydactyla and Cespitularia simplex surrounding Mauritius Island. Indo Pac J Ocean Life 7: 133-142. Soft corals form an integral part of the reef ecosystem. This study assessed the antibacterial activities of Mauritius Island's soft corals and their different natural compounds having important biological properties. Antimicrobial assays and GCMS-MS analysis were performed using ethyl acetate extracts of Sinularia polydactyla and Cespitularia simplex. The results for both species indicated significant activity against most clinically pathogenic bacterial strains tested. In addition, S. polydactyla and C. simplex extracts gave the most potent action spectra yielding the largest inhibition zone diameter, especially against the Gram-positive Staphylococcus aureus (8.73 ± 2.87 and 6.00 ± 1.20 mm), respectively. The MIC also confirmed that the Gram-positive Bacillus subtilis and S. aureus strains were the most susceptible bacteria when exposed to the soft coral extracts, while Pseudomonas aeruginosa and Escherichia coli were the most resistant Gram-negative strains. The biochemical profile of the extracts showed the presence of terpenoids, steroids, flavonoids, coumarins, and quinones. GCMS-MS analysis also identified 151 compounds in S. polydactyla and 91 compounds in C. simplex. Several previously published studies have shown the biological activities of different species of Cespitularia; however, this is the first study to demonstrate the antibacterial activity and compound profiling of C. simplex. Although studies have been carried out on S. polydactyla extracts, compounds such as 25-Hydroxycholesterol and spathulenol have not yet been reported. The results from the study suggest that both S. polydactyla and C. simplex are potential sources of novel antibiotics and possess a myriad of chemical compounds which may lend themselves to bioprospecting.