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Peer reviewed: True, Acknowledgements: The University of Mauritius is thanked for supporting the research and we extend our appreciation to the Researchers Supporting Project number (RSP-2021/218), King Saud University, Riyadh, Saudi Arabia., Marine fungi are largely associated with second most inhabitants of the marine ecosystem such as sponges and algae. They are important colonizers and play vital ecological roles, such as nutrient cycling, organic matter decomposition, and symbiosis with other organisms. High throughput sequencing methods have been used successfully to reveal unknown fungal communities associated with a number of hosts particularly in the marine environment. However, the diversity of marine fungi associated with sponges and brown algae in Mauritius remains largely unknown. Traditional methods based on culturing do not provide reliable estimate of fungal diversity as only those that are able to grow under laboratory conditions are dominant; in addition, a large proportion of fungi, cultured in vitro remain most of the time unidentifiable, given that there are no sporulating structures to be examined morphologically. To overcome these limitations, we employed Illumina sequencing to unravel fungi species present in the sponges, Iotrochota sp. and Biemna sp. and the brown algae Turbinaria conoides, Sargassum pfeifferae, and Sargassum obovatum, collected from the north of Mauritius. Diversity analyses revealed that Biemna sp. had the highest diversity from the sampled sponges with fungi from 24 orders being recovered while from brown algae; Turbinaria conoides had the highest diversity with recovery of fungal taxa of the orders Botryosphaeriales, Chaetothyriales, Eurotiales, Hypocreales, and Mucorales with the latter four orders being common in both sampled algae and sponges. Beta diversity analyses revealed clustering only in the algae, Turbinaria conoides, and Sargassum pfeifferae and not in the co-occurring sponges, indicating that sampling location did not have much influence on fungal diversity. Our findings provide the first amplicon sequencing based insights of the fungal communities associated with macro-algae and sponges in Mauritius and supplements research on the fungal community existing in the oceans around the world.

Background Some dinoflagellates cause harmful algal blooms, releasing toxic secondary metabolites, to the detriment of marine ecosystems and human health. Our understanding of dinoflagellate toxin biosynthesis has been hampered by their unusually large genomes. To overcome this challenge, for the first time, we sequenced the genome, microRNAs, and mRNA isoforms of a basal dinoflagellate, Amphidinium gibbosum, and employed an integrated omics approach to understand its secondary metabolite biosynthesis. Results We assembled the ~ 6.4-Gb A. gibbosum genome, and by probing decoded dinoflagellate genomes and transcriptomes, we identified the non-ribosomal peptide synthetase adenylation domain as essential for generation of specialized metabolites. Upon starving the cells of phosphate and nitrogen, we observed pronounced shifts in metabolite biosynthesis, suggestive of post-transcriptional regulation by microRNAs. Using Iso-Seq and RNA-seq data, we found that alternative splicing and polycistronic expression generate different transcripts for secondary metabolism. Conclusions Our genomic findings suggest intricate integration of various metabolic enzymes that function iteratively to synthesize metabolites, providing mechanistic insights into how dinoflagellates synthesize secondary metabolites, depending upon nutrient availability. This study provides insights into toxin production associated with dinoflagellate blooms. The genome of this basal dinoflagellate provides important clues about dinoflagellate evolution and overcomes the large genome size, which has been a challenge previously.

Photosynthetic dinoflagellates of the Family Symbiodiniaceae live symbiotically with many organisms that inhabit coral reefs and are currently classified into fifteen groups, including seven genera. Draft genomes from four genera, Symbiodinium, Breviolum, Fugacium, and Cladocopium, which have been isolated from corals, have been reported. However, no genome is available from the genus Durusdinium, which occupies an intermediate phylogenetic position in the Family Symbiodiniaceae and is well known for thermal tolerance (resistance to bleaching). We sequenced, assembled, and annotated the genome of Durusdinium trenchii, isolated from the coral, Favia speciosa, in Okinawa, Japan. Assembled short reads amounted to 670 Mb with ∼47% GC content. This GC content was intermediate among taxa belonging to the Symbiodiniaceae. Approximately 30,000 protein-coding genes were predicted in the D. trenchii genome, fewer than in other genomes from the Symbiodiniaceae. However, annotations revealed that the D. trenchii genome encodes a cluster of genes for synthesis of mycosporine-like amino acids, which absorb UV radiation. Interestingly, a neighboring gene in the cluster encodes a glucose–methanol–choline oxidoreductase with a flavin adenine dinucleotide domain that is also found in Symbiodinium tridacnidorum. This conservation seems to partially clarify an ancestral genomic structure in the Symbiodiniaceae and its loss in late-branching lineages, including Breviolum and Cladocopium, after splitting from the Durusdinium lineage. Our analysis suggests that approximately half of the taxa in the Symbiodiniaceae may maintain the ability to synthesize mycosporine-like amino acids. Thus, this work provides a significant genomic resource for understanding the genomic diversity of Symbiodiniaceae in corals.

Fluid chemistry and microbial community patterns in chimney habitats were investigated in two hydrothermal fields located at the Central Indian Ridge. Endmember hydrothermal fluid of the Solitaire field, located ~3 km away from the spreading center, was characterized by moderately high temperature (307°C), Cl depletion (489 mm), mildly acidic pH (≥4.40), and low metal concentrations (Fe ≤ 105 μm and Mn = 78 μm). Chloride depletion indicates that the subseafloor source fluid had undergone phase separation at temperatures higher than ~390°C while the metal depletion was likely attributable to fluid alteration occurring at a venting temperature of around 307°C. These different temperature conditions suggested from fluid chemistry might be associated with an off-spreading center location of the field that allows subseafloor fluid cooling prior to seafloor discharge. The microbial community in the chimney habitat seemed comparable to previously known patterns in typical basalt-hosted hydrothermal systems. Endmember hydrothermal fluid of the Dodo field, standing on center of the spreading axis, was characterized by high H2 concentration of 2.7 mm. The H2 enrichment was likely attributable to fresh basalt–fluid interaction, as suggested by the nondeformed sheet lava flow expansion around the vents. Thermodynamic calculation of the reducing pyrite–pyrrhotite–magnetite (PPM) redox buffer indeed reproduced the H2 enrichment. The quantitative cultivation test revealed that the microbial community associated with the hydrothermal fluid hosted abundant populations of (hyper)thermophilic hydrogenotrophic chemolithoautotrophs such as methanogens. The function of subseafloor hydrogenotrophic methanogenic populations dwelling around the H2-enriched hydrothermal fluid flows was also inferred from the 13C- and D-depleted signature of CH4 in the collected fluids. It was observed that the hydrothermal activity of the Dodo field had ceased until 2013.

Symbiotic dinoflagellates of the genus Symbiodinium are photosynthetic and unicellular. They possess smaller nuclear genomes than other dinoflagellates and produce structurally specialized, biologically active, secondary metabolites. Polyketide biosynthetic genes of toxic dinoflagellates have been studied extensively using transcriptomic analyses; however, a comparative genomic approach to understand secondary metabolism has been hampered by their large genome sizes. Here, we use a combined genomic and metabolomics approach to investigate the structure and diversification of secondary metabolite genes to understand how chemical diversity arises in three decoded Symbiodinium genomes (A3, B1 and C). Our analyses identify 71 polyketide synthase and 41 non-ribosomal peptide synthetase genes from two newly decoded genomes of clades A3 and C. Additionally, phylogenetic analyses indicate that almost all of the gene families are derived from lineage-specific gene duplications in Symbiodinium clades, suggesting divergence for environmental adaptation. Few metabolic pathways are conserved among the three clades and we detect metabolic similarity only in the recently diverged clades, B1 and C. We establish that secondary metabolism protein architecture guides substrate specificity and that gene duplication and domain shuffling have resulted in diversification of secondary metabolism genes.

Table S1. Summary of Illumina data used for assembling Symbiodinium genomes. Table S2. Summary of Illumina data used for assembling Symbiodinium transcriptomes. Table S3. Genomic compositions of three genomes of the genus Symbiodinium. Table S4. Summary of assembled transcriptome contigs. Table S5. Expanded genes having Pfam domains in SymA. Table S6. Expanded genes having Pfam domains in SymC. (DOCX 119 kb)

Over the past 40 years, there have been few reports describing marine natural product chemistry and related research from Mauritius. These came out from expeditions starting in the early 1970s by research groups of Dr. Petitt from the University of Arizona, followed by a latent phase to re-emerge as an area of potential scientific interest in early 2000s by investigation of the research group of Dr. Marie from the Mauritius Oceanography Institute. The natural product chemistry of Mauritius marine flora and fauna is relatively unknown and this review provides an overview of the contribution made by several groups towards the isolation, identification and bioactivity determination of these marine-derived natural products. The marine organisms reviewed include invertebrates, plants and microorganisms, emphasizing the biodiversity found in the vast Exclusive Economic Zone (EEZ) of Mauritius.

Patients diagnosed with Alzheimer's disease (AD) show a characteristic neurochemical deficit of acetylcholine, especially in the basal forebrains. The use of acetylcholinesterase (AChE) inhibitors to retard the hydrolysis of acetylcholine has been suggested as a promising strategy for AD treatment. In this study, we evaluated the acetylcholinesterase inhibitory (AChEI) activities of 134 extracts obtained from 45 species of marine sponges. Thin-layer chromatography (TLC) and microplate assays reveal potent acetylcholinsterase inhibitory activities of two AcOEt extracts from the sponges Pericharax heteroraphis and Amphimedon navalis PULITZER-FINALI. We further investigated the inhibitory kinetics of the extracts and found them to display mixed competitive/noncompetitive inhibition and associated their inhibitory activity partly to terpenoids. Acetylcholinesterase inhibitors from marine organisms have been rarely studied, and this study demonstrated the potential of marine sponges as a source of pharmaceutical leads against neurodegenerative diseases.

Figure S6. (A) NanoLC-MS (positive ion) profile of the methanol extract of Symbiodinium minutum. Top Chromatogram, Center Top: Extract ion (m/z 1072.60, 10.6Â min), Center bottom: (m/z 1050.57, 10.6Â min), Bottom: MS spectrum. (B) MS spectrum (positive ion) of the methanol extract (expanded). (PDF 145 kb)

Table S1. Predicted domains from transcriptome contigs Figure S1. Expression of KS domain-containing genes on scaffolds of S. minutum. Read coverages of RNAseq (gray line) on KS domain-containing genes (surrounded by green) show expression in our standard cultured conditions. In addition, the SL sequence containing reads (red line) from transcription start site (TSS) library suggest large multifunctional genes are expressed as a transcript that is not trans-spliced. Red arrows show trans-spliced sites, located internally in KS domain-containing genes. Figure S2. Molecular phylogenetic tree of Type I and Type II KS domains from prokaryotic and eukaryotic PKS and FAS, analyzed by maximum likelihood. Type II KS and acyl carrier protein synthases (ACPS) were used as outgroups. Bootstrap values ≥ 50 % are marked at appropriate nodes. Details regarding S. minutum sequences are provided in Table 1. (PDF 9386 kb)

Figure S3. (A) Alignment of KS domains with those of other dinoflagellates and animal PKSs and FASs. Asterisks indicate conserved amino acids required for catalytic activity. (B) Additional Symbiodinium and K. brevis sequences that are consistent with previous reports. Figure S4. Alignments of motifs within AT, ACP, KR, ER, and DH domains. Active sites within the motifs are boxed with dashed lines. Figure S5. (A) Multiple alignment of the truncated, conserved, N-termini of dinoflagellate KSs (B) Additional Symbiodinium sequences with the divergent signatures. Lower panel: Maximum likelihood tree of the N-termini computed with 1000 bootstrap replicates. Bootstrap values ≥ 50 % are marked at appropriate nodes. (PDF 2705 kb)

A new species of the alvinocaridid shrimp genus Alvinocaris WilliamsChace, 1982 is described from the Solitaire hydrothermal vent field at 2606 m depth on the Central Indian Ridge. Alvinocaris solitaire sp. nov., the first species of the genus to be recorded from the Indian Ocean, is morphologically most similar to A. lusca WilliamsChace, 1982 from the Galapagos Rift, East Pacific Rise. The new species is distinguished from A. lusca by the less produced pterygostomial angle of the carapace, the presence of small teeth on the posterolateral margin of the third pleuron, and the lack of short plumose setae on the posteromedian margin of the telson. The genetic divergence of the mitochondrial cytochrome c oxidase subunit I (COI) gene (600 bp) among the nine Alvinocaris species analyzed clearly indicates that the new taxon is distinct from the congeneric species for which genetic data are available.

In deep-sea hydrothermal vent fields, faunal distribution is associated with the geochemical environments generated by hydrothermal vent activity. Hydrothermal vent fields on the Central Indian Ridge (CIR) are associated with vent fauna which is thought as a mixture of Atlantic and Pacific and are discretely distributed along the ridge axis of more than 1,000 km apart. In this chapter, faunal distribution in hydrothermal vent fields on the CIR is summarized at the intra- and inter-field levels. The species composition of the vent fauna in the four vent fields hitherto known is reviewed and updated, and faunal resemblance among the four vent fields of the CIR appears to reflect the number of species recorded, indicating that faunal surveys are not sufficient in describing the whole vent fauna on the CIR. All the genetic studies of the CIR vent fauna have indicated a high genetic connectivity among the local populations, despite the many potential dispersal barriers existing between the vent fields. On the basis of the spatial distribution of vent species in a vent field, typical vent fields on the CIR were classified into six zones, of which the central two zones are often covered by Rimicaris swarms in the Kairei and Edmond fields. The close relationship between vent fauna from the CIR and the western Pacific, compared to those from other regions, is highlighted. Knowledge of the Indian Ocean vent fauna is limited, and further quantitative information on the biodiversity of vent fauna will provide clues to the formation of biogeographical regions and the dispersal of vent fauna among deep-sea hydrothermal vent fields.

International audience; Marine sponges are considered as a gold mine of new natural products possessing numerous biological activities. We examined the cytotoxic properties of the ethyl acetate extract (JDE) of the previously unrecorded sponge, Jaspis sp. collected from Mauritius Waters. JDE displayed an interesting IC50 of 0.057±0.04μg/mL on HL-60 cells evaluated by MTS assay. Mitochondrial membrane potential change, microscopic analysis and DNA fragmentation assays also confirmed JDE induced apoptosis on HL-60 cells. Annexin V staining demonstrated that JDE induced apoptosis at different concentrations. Treatment with 100ng/mL of JDE led to an accumulation of cells in G2/M phase after 24 h, causing a significant increase of cells (24h: 5.84%; 48h: 13.41%) in sub-G1 phase suggesting that JDE can induce cell cycle arrest in G2/M phase.

International audience; The ocean is an exceptional source of natural products with many of them exhibiting novel structural features and bioactivity. As one of the most interesting phylum with respect to pharmacological active marine compounds, Poriferas have been investigated widely in the last few decades. A total of 60 organic extracts (hexane, ethyl acetate and butanol) from 20 species of marine sponges from Mauritius were screened at 50μg/ml in an in vitro screening assay against 9 human cancer cell lines. From these tested extracts, many exhibited pronounced cytotoxic effect at least in one of the cell lines and cell type cytotoxic specificity was observed. 27% of ethyl acetate, 11% of hexane and 2% of butanol extracts were found to possess a cytotoxicity ≥75% on 9 different cancer cell lines with the sponges Petrosia sp. 1, Petrosia sp. 2, Pericharax heteroraphis and Jaspis sp. being the most active. Overall, the HL-60cells were much more sensitive to most of the extracts than the other cell lines. We further evaluated the properties of the ethyl acetate (JDE) and hexane extract (JDH) of one sponge, Jaspis sp. on KB cells. JDE displayed a smaller IC(50) than JDH. Clonogenic assay confirmed the antiproliferative effect of both extracts while mitochondrial membrane potential change and microscopic analysis demonstrated extracts-induced apoptosis. Treatment with 100ng/ml of JDE led to a significant increase of cells (24h: 4.02%; 48h: 26.23%) in sub-G1 phase. The cytotoxic properties of the tested extracts from these sponges suggest the presence of compounds with pharmacological potential and are currently undergoing fractionation to isolate the active constituents.

A new species of the alvinocaridid shrimp genus Alvinocaris Williams & Chace, 1982 is described from the Solitaire hydrothermal vent field at 2606 m depth on the Central Indian Ridge. Alvinocaris solitaire sp. nov., the first species of the genus to be recorded from the Indian Ocean, is morphologically most similar to A. lusca Williams & Chace, 1982 from the Galapagos Rift, East Pacific Rise. The new species is distinguished from A. lusca by the less produced pterygostomial angle of the carapace, the presence of small teeth on the posterolateral margin of the third pleuron, and the lack of short plumose setae on the posteromedian margin of the telson. The genetic divergence of the mitochondrial cytochrome c oxidase subunit I (COI) gene (600 bp) among the nine Alvinocaris species analyzed clearly indicates that the new taxon is distinct from the congeneric species for which genetic data are available.

As part of our ongoing studies on bioactive natural products from marine sponges, we investigated the cytotoxic potential of extracts from the new sponge Petrosia tuberosa sampled from Mauritius waters. Bioguided fractionation of the ethyl acetate extract by vacuum liquid chromatography (VLC) revealed two fractions, namely VLC (6-9) and (13-17) showing cell deaths of 86 ± 1% and 88 ± 4%, respectively, at 50 μg/mL on HeLa cells. At 10 μg/mL, only VLC (13-17) displayed a significant cell death (56 ± 7%) compared with VLC (6-9) (8 ± 1 %). The cytotoxic activity of VLC (13-17) was also determined on nine other human cancer cell lines. Clonogenic assay, mitochondrial membrane potential change, DNA fragmentation and microscopic analysis of fraction VLC (13-17) revealed distinct features of apoptosis on HeLa cells. Further fractionation and purification of this fraction by chromatographic techniques resulted in isolation of one known secondary metabolite, petrosynol. Its structure was determined by 1H and 13C-NMR analyses.

This report describes the use of α-glucosidase to evaluate the anti-diabetic potential of extracts from marine sponges collected in the Mauritius waters. Initial screening at 1.0 mg/mL of 141 extracts obtained from 47 sponge species revealed 10 extracts with inhibitory activity greater than 85%. Seven of the 10 extracts were further tested at 0.1 and 0.01 mg/mL and only the methanol extract of two sponges namely Acanthostylotella sp. (ASSM) and Echinodictyum pykei (EPM) showed inhibition activity greater than 60% at 0.1 mg/mL with an IC50 value of 0.16 ± 0.02 and 0.04 ± 0.01 mg/mL, respectively, while being inactive at 0.01 mg/mL.

This report describes the use of α-glucosidase to evaluate the anti-diabetic potential of extracts from marine sponges collected in the Mauritius waters. Initial screening at 1.0 mg/mL of 141 extracts obtained from 47 sponge species revealed 10 extracts with inhibitory activity greater than 85%. Seven of the 10 extracts were further tested at 0.1 and 0.01 mg/mL and only the methanol extract of two sponges namely Acanthostylotella sp. (ASSM) and Echinodictyum pykei (EPM) showed inhibition activity greater than 60% at 0.1 mg/mL with an IC50 value of 0.16 ± 0.02 and 0.04 ± 0.01 mg/mL, respectively, while being inactive at 0.01 mg/mL.

This report describes the use of α-glucosidase to evaluate the anti-diabetic potential of extracts from marine sponges collected in the Mauritius waters. Initial screening at 1.0 mg/mL of 141 extracts obtained from 47 sponge species revealed 10 extracts with inhibitory activity greater than 85%. Seven of the 10 extracts were further tested at 0.1 and 0.01 mg/mL and only the methanol extract of two sponges namely Acanthostylotella sp. (ASSM) and Echinodictyum pykei (EPM) showed inhibition activity greater than 60% at 0.1 mg/mL with an IC50 value of 0.16 ± 0.02 and 0.04 ± 0.01 mg/mL, respectively, while being inactive at 0.01 mg/mL.