Differences in carbonate chemistry up-regulation of long-lived reef-building corals

With climate projections questioning the future survival of stony corals and their dominance as tropical reef builders, it is critical to understand the adaptive capacity of corals to ongoing climate change. Biological mediation of the carbonate chemistry of the coral calcifying fluid is a fundamental component for assessing the response of corals to global threats. The Tara Pacific expedition (2016-2018) provided an opportunity to investigate calcification patterns in extant corals throughout the Pacific Ocean. Cores from colonies of the massive Porites and Diploastrea genera were collected from different environments to assess calcification parameters of long-lived reef-building corals. At the basin scale of the Pacific Ocean, we show that both genera systematically up-regulate their calcifying fluid pH and dissolved inorganic carbon to achieve efficient skeletal precipitation. However, while Porites corals increase the aragonite saturation state of the calcifying fluid (Ω_cf) at higher temperatures to enhance their calcification capacity, Diploastrea show a steady homeostatic Ω_cf across the Pacific temperature gradient. Thus, the extent to which Diploastrea responds to ocean warming and/or acidification is unclear, and it deserves further attention whether this is beneficial or detrimental to future survival of this coral genus.

Ecology of Endozoicomonadaceae in three coral genera across the Pacific Ocean

Health and resilience of the coral holobiont depend on diverse bacterial communities often dominated by key marine symbionts of the Endozoicomonadaceae family. The factors controlling their distribution and their functional diversity remain, however, poorly known. Here, we study the ecology of Endozoicomonadaceae at an ocean basin-scale by sampling specimens from three coral genera (Pocillopora, Porites, Millepora) on 99 reefs from 32 islands across the Pacific Ocean. The analysis of 2447 metabarcoding and 270 metagenomic samples reveals that each coral genus harbored a distinct new species of Endozoicomonadaceae. These species are composed of nine lineages that have distinct biogeographic patterns. The most common one, found in Pocillopora, appears to be a globally distributed symbiont with distinct metabolic capabilities, including the synthesis of amino acids and vitamins not produced by the host. The other lineages are structured partly by the host genetic lineage in Pocillopora and mainly by the geographic location in Porites. Millepora is more rarely associated to Endozoicomonadaceae. Our results show that different coral genera exhibit distinct strategies of host-Endozoicomonadaceae associations that are defined at the bacteria lineage level.

Telomere DNA length regulation is influenced by seasonal temperature differences in short-lived but not in long-lived reef-building corals

Telomeres are environment-sensitive regulators of health and aging. Here,we present telomere DNA length analysis of two reef-building coral genera revealing that the long- and short-term water thermal regime is a key driver of between-colony variation across the Pacific Ocean. Notably, there are differences between the two studied genera. The telomere DNA lengths of the short-lived, more stress-sensitive Pocillopora spp. colonies were largely determined by seasonal temperature variation, whereas those of the long-lived, more stress-resistant Porites spp. colonies were insensitive to seasonal patterns, but rather influenced by past thermal anomalies. These results reveal marked differences in telomere DNA length regulation between two evolutionary distant coral genera exhibiting specific life-history traits. We propose that environmentally regulated mechanisms of telomere maintenance are linked to organismal performances, a matter of paramount importance considering the effects of climate change on health.

Open science resources from the Tara Pacific expedition across coral reef and surface ocean ecosystems

The Tara Pacific expedition (2016-2018) sampled coral ecosystems around 32 islands in the Pacific Ocean and the ocean surface waters at 249 locations, resulting in the collection of nearly 58 000 samples. The expedition was designed to systematically study warm-water coral reefs and included the collection of corals, fish, plankton, and seawater samples for advanced biogeochemical, molecular, and imaging analysis. Here we provide a complete description of the sampling methodology, and we explain how to explore and access the different datasets generated by the expedition. Environmental context data were obtained from taxonomic registries, gazetteers, almanacs, climatologies, operational biogeochemical models, and satellite observations. The quality of the different environmental measures has been validated not only by various quality control steps, but also through a global analysis allowing the comparison with known environmental large-scale structures. Such publicly released datasets open the perspective to address a wide range of scientific questions.

Endogenous viral elements reveal associations between a non-retroviral RNA virus and symbiotic dinoflagellate genomes

Endogenous viral elements (EVEs) offer insight into the evolutionary histories and hosts of contemporary viruses. This study leveraged DNA metagenomics and genomics to detect and infer the host of a non-retroviral dinoflagellate-infecting +ssRNA virus (dinoRNAV) common in coral reefs. As part of the Tara Pacific Expedition, this study surveyed 269 newly sequenced cnidarians and their resident symbiotic dinoflagellates (Symbiodiniaceae), associated metabarcodes, and publicly available metagenomes, revealing 178 dinoRNAV EVEs, predominantly among hydrocoral-dinoflagellate metagenomes. Putative associations between Symbiodiniaceae and dinoRNAV EVEs were corroborated by the characterization of dinoRNAV-like sequences in 17 of 18 scaffold-scale and one chromosome-scale dinoflagellate genome assembly, flanked by characteristically cellular sequences and in proximity to retroelements, suggesting potential mechanisms of integration. EVEs were not detected in dinoflagellate-free (aposymbiotic) cnidarian genome assemblies, including stony corals, hydrocorals, jellyfish, or seawater. The pervasive nature of dinoRNAV EVEs within dinoflagellate genomes (especially Symbiodinium), as well as their inconsistent within-genome distribution and fragmented nature, suggest ancestral or recurrent integration of this virus with variable conservation. Broadly, these findings illustrate how +ssRNA viruses may obscure their genomes as members of nested symbioses, with implications for host evolution, exaptation, and immunity in the context of reef health and disease.

Diversity of the Pacific Ocean coral reef microbiome

Coral reefs are among the most diverse ecosystems on Earth. They support high biodiversity of multicellular organisms that strongly rely on associated microorganisms for health and nutrition. However, the extent of the coral reef microbiome diversity and its distribution at the oceanic basin-scale remains to be explored. Here, we systematically sampled 3 coral morphotypes, 2 fish species, and planktonic communities in 99 reefs from 32 islands across the Pacific Ocean, to assess reef microbiome composition and biogeography. We show a very large richness of reef microorganisms compared to other environments, which extrapolated to all fishes and corals of the Pacific, approximates the current estimated total prokaryotic diversity for the entire Earth. Microbial communities vary among and within the 3 animal biomes (coral, fish, plankton), and geographically. For corals, the cross-ocean patterns of diversity are different from those known for other multicellular organisms. Within each coral morphotype, community composition is always determined by geographic distance first, both at the island and across ocean scale, and then by environment. Our unprecedented sampling effort of coral reef microbiomes, as part of the Tara Pacific expedition, provides new insight into the global microbial diversity, the factors driving their distribution, and the biocomplexity of reef ecosystems.

Integrative omics framework for characterization of coral reef ecosystems from the Tara Pacific expedition

Coral reef science is a fast-growing field propelled by the need to better understand coral health and resilience to devise strategies to slow reef loss resulting from environmental stresses. Key to coral resilience are the symbiotic interactions established within a complex holobiont, i.e. the multipartite assemblages comprising the coral host organism, endosymbiotic dinoflagellates, bacteria, archaea, fungi, and viruses. Tara Pacific is an ambitious project built upon the experience of previous Tara Oceans expeditions, and leveraging state-of-the-art sequencing technologies and analyses to dissect the biodiversity and biocomplexity of the coral holobiont screened across most archipelagos spread throughout the entire Pacific Ocean. Here we detail the Tara Pacific workflow for multi-omics data generation, from sample handling to nucleotide sequence data generation and deposition. This unique multidimensional framework also includes a large amount of concomitant metadata collected side-by-side that provide new assessments of coral reef biodiversity including micro-biodiversity and shape future investigations of coral reef dynamics and their fate in the Anthropocene.

Pervasive tandem duplications and convergent evolution shape coral genomes

BACKGROUND

Over the last decade, several coral genomes have been sequenced allowing a better understanding of these symbiotic organisms threatened by climate change. Scleractinian corals are reef builders and are central to coral reef ecosystems, providing habitat to a great diversity of species.

RESULTS

In the frame of the Tara Pacific expedition, we assemble two coral genomes, Porites lobata and Pocillopora cf. effusa, with vastly improved contiguity that allows us to study the functional organization of these genomes. We annotate their gene catalog and report a relatively higher gene number than that found in other public coral genome sequences, 43,000 and 32,000 genes, respectively. This finding is explained by a high number of tandemly duplicated genes, accounting for almost a third of the predicted genes. We show that these duplicated genes originate from multiple and distinct duplication events throughout the coral lineage. They contribute to the amplification of gene families, mostly related to the immune system and disease resistance, which we suggest to be functionally linked to coral host resilience.

CONCLUSIONS

At large, we show the importance of duplicated genes to inform the biology of reef-building corals and provide novel avenues to understand and screen for differences in stress resilience.

Host transcriptomic plasticity and photosymbiotic fidelity underpin Pocillopora acclimatization across thermal regimes in the Pacific Ocean

Heat waves are causing declines in coral reefs globally. Coral thermal responses depend on multiple, interacting drivers, such as past thermal exposure, endosymbiont community composition, and host genotype. This makes the understanding of their relative roles in adaptive and/or plastic responses crucial for anticipating impacts of future warming. Here, we extracted DNA and RNA from 102 Pocillopora colonies collected from 32 sites on 11 islands across the Pacific Ocean to characterize host-photosymbiont fidelity and to investigate patterns of gene expression across a historical thermal gradient. We report high host-photosymbiont fidelity and show that coral and microalgal gene expression respond to different drivers. Differences in photosymbiotic association had only weak impacts on host gene expression, which was more strongly correlated with the historical thermal environment, whereas, photosymbiont gene expression was largely determined by microalgal lineage. Overall, our results reveal a three-tiered strategy of thermal acclimatization in Pocillopora underpinned by host-photosymbiont specificity, host transcriptomic plasticity, and differential photosymbiotic association under extreme warming.

Thirtieth Anniversary of the Discovery of Laxaphycins. Intriguing Peptides Keeping a Part of Their Mystery

Lipopeptides are a class of compounds generally produced by microorganisms through hybrid biosynthetic pathways involving non-ribosomal peptide synthase and a polyketyl synthase. Cyanobacterial-produced laxaphycins are examples of this family of compounds that have expanded over the past three decades. These compounds benefit from technological advances helping in their synthesis and characterization, as well as in deciphering their biosynthesis. The present article attempts to summarize most of the articles that have been published on laxaphycins. The current knowledge on the ecological role of these complex sets of compounds will also be examined.

Coral larval settlement preferences linked to crustose coralline algae with distinct chemical and microbial signatures

The resilience of coral reefs is dependent on the ability of corals to settle after disturbances. While crustose coralline algae (CCA) are considered important substrates for coral settlement, it remains unclear whether coral larvae respond to CCA metabolites and microbial cues when selecting sites for attachment and metamorphosis. This study tested the settlement preferences of an abundant coral species (Acropora cytherea) against six different CCA species from three habitats (exposed, subcryptic and cryptic), and compared these preferences with the metabolome and microbiome characterizing the CCA. While all CCA species induced settlement, only one species (Titanoderma prototypum) significantly promoted settlement on the CCA surface, rather than on nearby dead coral or plastic surfaces. This species had a very distinct bacterial community and metabolomic fingerprint. Furthermore, coral settlement rates and the CCA microbiome and metabolome were specific to the CCA preferred habitat, suggesting that microbes and/or chemicals serve as environmental indicators for coral larvae. Several amplicon sequence variants and two lipid classes—glycoglycerolipids and betaine lipids—present in T. prototypum were identified as potential omic cues influencing coral settlement. These results support that the distinct microbiome and metabolome of T. prototypum may promote the settlement and attachment of coral larvae.

d-Peptidase Activity in a Marine Mollusk Detoxifies a Nonribosomal Cyclic Lipopeptide: An Ecological Model to Study Antibiotic Resistance

In the marine environment, sessile cyanobacteria have developed chemical strategies for protection against grazers. In turn, herbivores have to circumvent these defenses and in certain cases even take advantage of them as shelter from their own predators. This is the case of Stylocheilus striatus, a sea hare that feeds on Anabaena torulosa, a cyanobacterium that produces toxic cyclic lipopeptides of the laxaphycin B family. S. striatus consumes the cyanobacterium without being affected by the toxicity of its compounds and also uses it as an invisibility cloak against predators. In this article, using different substrates analogous to laxaphycin B, we demonstrate the presence of an enzyme in the digestive gland of the mollusk that is able to biotransform laxaphycin B derivatives. The enzyme belongs to the poorly known family of d-peptidases that are suspected to be involved in antibiotic resistance.

Antifouling Activity of Meroterpenes Isolated from the Ascidian Aplidium aff. densum

The settlement and growth of fouling organisms on man-made surfaces can be prevented by the application of antifouling paints containing active compounds (biocides, heavy metals), most of which are toxic to non-target organisms. As part of our research program in chemical ecology and blue biotechnology, we are conducting studies to investigate the natural defence mechanisms of marine organisms that are free from epibionts, with the aim of isolating molecules involved in surface defence that could be good candidates as antifouling agents. Ascidians were selected for our investigation because previous studies have shown that they contain abundant and diverse secondary metabolites, which play a defensive role and have been applied to drug discovery. It is therefore relevant to study the role of such secondary metabolites in surface protection. In this study, 5 meroterpenoids (cordiachromene A, didehydroconicol, epiconicol, methoxyconidiol, conidione) from Aplidium aff. densum (ascidian) were investigated as potential antifoulants towards the inhibition of bacterial growth and settlement inhibition of barnacles. Cardiochromene A (IC₅₀ barnacle settlement = 6.04 μg/mL; MIC Gram positive = 125 μg/mL; MIC Gram negative = 32 μg/mL) and epiconicol (IC₅₀ barnacle settlement = 8.05 μg/mL; MIC Bacillus = 63 μg/mL; MIC other strains = 32 μg/mL) were the most promising compounds among those tested in this study.

Biological Activities of Cyclic and Acyclic B-Type Laxaphycins in SH-SY5Y Human Neuroblastoma Cells

Laxaphycins are a family of non-ribosomal lipopeptides that have been isolated from several cyanobacteria. Some of these compounds have presented cytotoxic activities, but their mechanism of action is poorly understood. In this work, the already described laxaphycins B and B3, and acyclolaxaphycins B and B3 were isolated from the marine cyanobacteria Anabaena torulosa. Moreover, two new acyclic compounds, [des-(Ala⁴-Hle⁵)] acyclolaxaphycins B and B3, were purified from the herviborous gastropod Stylocheilus striatus, with this being the first description of biotransformed laxaphycins. The structure of these new compounds was elucidated, together with the absolute configuration of acyclolaxaphycins B and B3. The bioactivities of the six peptides were determined in SH-SY5Y human neuroblastoma cells. Laxaphycins B and B3 were cytotoxic (IC₅₀: 1.8 and 0.8 µM, respectively) through the induction of apoptosis. In comparison, acyclic laxaphycins did not show cytotoxicity but affected mitochondrial functioning, so their effect on autophagy-related protein expression was analyzed, finding that acyclic peptides affected this process by increasing AMPK phosphorylation and inhibiting mTOR. This work confirms the pro-apoptotic properties of cyclic laxaphycins B and is the first report indicating the effects on autophagy of their acyclic analogs. Moreover, gastropod-derived compounds presented ring opening and amino-acids deletion, a biotransformation that had not been previously described.

Insights into the Natural Defenses of a Coral Reef Fish Against Gill Ectoparasites: Integrated Metabolome and Microbiome Approach

Understanding natural defense mechanisms against parasites can be a valuable tool for the development of innovative therapies. We have previously identified a butterflyfish species (Chaetodon lunulatus) that avoids gill monogenean parasites while living amongst closely related parasitized species. The metabolome and microbiome of several sympatric butterflyfish species from the island of Moorea (French Polynesia) were previously described. In this study, we used the previously generated datasets in an attempt to identify metabolites and bacteria potentially involved in parasite defense mechanisms. We investigated the interplay between the gill mucus metabolome and microbiome of the non-susceptible C. lunulatus versus sympatric butterflyfish species that were always found parasitized in the Central and Eastern Indo-Pacific. After observing significant differences between the metabolome and bacteria of susceptible versus non-susceptible fish, we obtained the discriminant metabolites and operational taxonomic units (OTUs) using a supervised analysis. Some of the most important discriminant metabolites were identified as peptides, and three new peptides derived from β-subunit hemoglobin from C. lunulatus (CLHbβ-1, CLHbβ-2, and CLHbβ-3) were purified, characterized and synthesized to confirm their structures. We also identified specific bacterial families and OTUs typical from low-oxygen habitats in C. lunulatus gill mucus. By using a correlation network between the two datasets, we found a Fusobacteriaceae strain exclusively present in C. lunulatus and highly correlated to the peptides. Finally, we discuss the possible involvement of these peptides and Fusobacteriaceae in monogenean avoidance by this fish species.

The Tara Pacific expedition-A pan-ecosystemic approach of the "-omics" complexity of coral reef holobionts across the Pacific Ocean

Coral reefs are the most diverse habitats in the marine realm. Their productivity, structural complexity, and biodiversity critically depend on ecosystem services provided by corals that are threatened because of climate change effects-in particular, ocean warming and acidification. The coral holobiont is composed of the coral animal host, endosymbiotic dinoflagellates, associated viruses, bacteria, and other microeukaryotes. In particular, the mandatory photosymbiosis with microalgae of the family Symbiodiniaceae and its consequences on the evolution, physiology, and stress resilience of the coral holobiont have yet to be fully elucidated. The functioning of the holobiont as a whole is largely unknown, although bacteria and viruses are presumed to play roles in metabolic interactions, immunity, and stress tolerance. In the context of climate change and anthropogenic threats on coral reef ecosystems, the Tara Pacific project aims to provide a baseline of the "-omics" complexity of the coral holobiont and its ecosystem across the Pacific Ocean and for various oceanographically distinct defined areas. Inspired by the previous Tara Oceans expeditions, the Tara Pacific expedition (2016-2018) has applied a pan-ecosystemic approach on coral reefs throughout the Pacific Ocean, drawing an east-west transect from Panama to Papua New Guinea and a south-north transect from Australia to Japan, sampling corals throughout 32 island systems with local replicates. Tara Pacific has developed and applied state-of-the-art technologies in very-high-throughput genetic sequencing and molecular analysis to reveal the entire microbial and chemical diversity as well as functional traits associated with coral holobionts, together with various measures on environmental forcing. This ambitious project aims at revealing a massive amount of novel biodiversity, shedding light on the complex links between genomes, transcriptomes, metabolomes, organisms, and ecosystem functions in coral reefs and providing a reference of the biological state of modern coral reefs in the Anthropocene.

Structures and Activities of Tiahuramides A-C, Cyclic Depsipeptides from a Tahitian Collection of the Marine Cyanobacterium Lyngbya majuscula

The structures of three new cyclic depsipeptides, tiahuramides A (1), B (2), and C (3), from a French Polynesian collection of the marine cyanobacterium Lyngbya majuscula are described. The planar structures of these compounds were established by a combination of mass spectrometry and 1D and 2D NMR experiments. Absolute configurations of natural and nonproteinogenic amino acids were determined through a combination of acid hydrolysis, derivitization with Marfey's reagent, and HPLC. The absolute configuration of hydroxy acids was confirmed by Mosher's method. The antibacterial activities of tiahuramides against three marine bacteria were evaluated. Compound 3 was the most active compound of the series, with an MIC of 6.7 μM on one of the three tested bacteria. The three peptides inhibit the first cell division of sea urchin fertilized eggs with IC₅₀ values in the range from 3.9 to 11 μM. Tiahuramide B (2), the most potent compound, causes cellular alteration characteristics of apoptotic cells, blebbing, DNA condensation, and fragmentation, already at the first egg cleavage. The cytotoxic activity of compounds 1-3 was tested in SH-SY5Y human neuroblastoma cells. Compounds 2 and 3 showed an IC₅₀ of 14 and 6.0 μM, respectively, whereas compound 1 displayed no toxicity in this cell line at 100 μM. To determine the type of cell death induced by tiahuramide C (3), SH-SY5Y cells were costained with annexin V-FITC and propidium iodide and analyzed by flow cytometry. The double staining indicated that the cytotoxicity of compound 3 in this cell line is produced by necrosis.

Habitat selection by marine larvae in changing chemical environments

The replenishment and persistence of marine species is contingent on dispersing larvae locating suitable habitat and surviving to a reproductive stage. Pelagic larvae rely on environmental cues to make behavioural decisions with chemical information being important for habitat selection at settlement. We explored the sensory world of crustaceans and fishes focusing on the impact anthropogenic alterations (ocean acidification, red soil, pesticide) have on conspecific chemical signals used by larvae for habitat selection. Crustacean (Stenopus hispidus) and fish (Chromis viridis) larvae recognized their conspecifics via chemical signals under control conditions. In the presence of acidified water, red soil or pesticide, the ability of larvae to chemically recognize conspecific cues was altered. Our study highlights that recruitment potential on coral reefs may decrease due to anthropogenic stressors. If so, populations of fishes and crustaceans will continue their rapid decline; larval recruitment will not replace and sustain the adult populations on degraded reefs.

Chemical mediation as a structuring element in marine gastropod predator-prey interactions

Some diterpenoid compounds protect the sacoglossansElysiasp. andCyerce nigricansfrom their carnivorous predator the dorid nudibranch,Gymnodorissp., unlike chemically unprotected gastropods that are consumed by this voracious nudibranch (photo Philippe Bourseiller).

Chemical spying in coral reef fish larvae at recruitment

When fish larvae recruit back to a reef, chemical cues are often used to find suitable habitat or to find juvenile or adult conspecifics. We tested if the chemical information used by larvae was intentionally produced by juvenile and adult conspecifics already on the reef (communication process) or whether the cues used result from normal biochemical processes with no active involvement by conspecifics ("spying" behavior by larvae). Conspecific chemical cues attracted the majority of larvae (four out of the seven species tested); although while some species were equally attracted to cues from adults and juveniles (Chromis viridis, Apogon novemfasciatus), two exhibited greater sensitivity to adult cues (Pomacentrus pavo, Dascyllus aruanus). Our results indicate also that spying cues are those most commonly used by settling fishes (C. viridis, P. pavo, A. novemfasciatus). Only one species (D. aruanus) preferred the odour of conspecifics that had had visual contact with larvae (communication).

Additional cytotoxic pyridoacridine alkaloids from the ascidian Cystodytes violatinctus and biogenetic considerations

The extraction and purification of the bioactive extract of Cystodytes violatinctus (Solomon Islands) led to the isolation and identification of six pyridoacridine alkaloids. The structures of four new members of this family, shermilamine F (1), dehydrokuanoniamine F (2), and arnoamines C (3) and D (4), were elucidated on the basis of NMR and MS data and by comparison with data of known compounds isolated from this genus. A general hypothetical biogenetic pathway is then proposed for pyridoacridine alkaloids that contain a fused pyrrole ring. Comparison of the biological properties of the isolated alkaloids is also discussed.

Sources of secondary metabolite variation in Dysidea avara (Porifera: Demospongiae): the importance of having good neighbors

Several studies report temporal, geographical, and intra-individual variation in sponge metabolite yields. However, the internal and/or external factors that regulate the metabolite production remain poorly understood. Dysidea avara is a demosponge that produces sesquiterpenoids (avarol and derivatives) with interesting medical properties, which has prompted addressed studies to obtain enough amounts of these metabolites for research on drug discovery. Within this framework, specimens of Dysidea avara from apopulation of the Northwest Mediterranean were sampled and their secondary metabolites quantified to assess their variability and the possible relationship with external (seasonality, interactions with neighbors) and internal (reproductive stages) factors. The results show a variation of the amount of both avarol and its monoacetate derivative with time, with no clear relationship with seawater temperature. A trade-off with sponge reproduction was not found either. However, our results showed for the first time that sponges are able to increase production or accumulation of secondary metabolites in their peripheral zone depending on the nature of their neighbors. This finding could explain part of the high variability in the amount of secondary metabolites usually found in chemical ecology studies on sponges and opens new biotechnological approaches to enhance the metabolite yield in sponge cultures.

Temporal trends in the secondary metabolite production of the sponge Aplysina aerophoba

Temporal changes in the production of secondary metabolites are far from being fully understood. Our study quantified, over a two-year period, the concentrations of brominated alkaloids in the ectosome and the choanosome of Aplysina aerophoba, and examined the temporal patterns of these natural products. Based on standard curves, we quantified the concentrations of aerophobin-2, aplysinamisin-1, and isofistularin-3: three of the four major peaks obtained through chemical profiling with high-performance liquid chromatography. Our results showed a striking variation in compound abundance between the outer and inner layers of the sponge. The ectosome showed high concentrations of bromocompounds during the summer months, while the choanosome followed no pattern. Additionally, we found that, from the outer layer of the sponge, aerophobin-2 and isofistularin-3 were significantly correlated with water temperature. The present study is one of the first to document quantitative seasonal variations in individual compounds over multiple years. Further studies will clarify the role of environmental, biological, and physiological factors in determining the seasonal patterns in the concentration of brominated alkaloids.

Relevance of an integrative approach for taxonomic revision in sponge taxa: case study of the shallow-water Atlanto-Mediterranean Hexadella species (Porifera:Ianthellidae:Verongida)

The identification of sponges that lack a mineral skeleton is always highly challenging, especially for Hexadella species, which are also fibreless. Recently, the yellow species Hexadella pruvoti Topsent was identified as a cryptic species complex while the pink coloured Hexadella racovitzai Topsent showed two highly divergent lineages. We performed a COI phylogenetic reconstruction using 27 new Mediterranean Hexadella samples in order to confirm the presence of divergent lineages within both shallow-water species. Specimens were described with an integrative approach combining morphological and cytological investigations, biochemical profiling and assessment of natural toxicity in order to identify diagnostic characters for each taxon. H. topsenti, sp. nov. is distinguished from H. racovitzai by its colour, its surface network shape, divergent secondary metabolite patterns and toxicity values. H. crypta, sp. nov. differs from H. pruvoti by a different encrusting growth form when alive, and by distinctively colouring the ethanol fixative solution. In addition, H. pruvoti and H. crypta show different types of cells with inclusions as well as distinct metabolic fingerprints. Natural toxicity values, however, do not permit the separation of H. pruvoti and H. crypta. Our work shows that only the use of a combination of complementary tools can provide relevant descriptions for some problematic taxa.

Structures and antimicrobial activities of pyridoacridine alkaloids isolated from different chromotypes of the ascidian Cystodytes dellechiajei

Three new pentacyclic alkaloids were isolated from different chromotypes of the western Mediterranean ascidian Cystodytes dellechiajei. The purple color morph collected in Catalonia contained the known compounds kuanoniamine D (1), shermilamine B (2), N-deacetylkuanoniamine D (3), and styelsamine C (4) and a new alkaloid named N-deacetylshermilamine B (5). The green color morph collected in the Balearic Islands contained the known compounds 11-hydroxyascididemin (6) and 8,9-dihydro-11-hydroxyascididemin (7) and two new alkaloids named cystodimine A (8) and cystodimine B (9). The blue color morph collected in Catalonia yielded the known compound ascididemin (10). The structures of all compounds were elucidated on the basis of spectroscopic data, mainly 1D and 2D NMR data. The antimicrobial potential of the pyridoacridine alkaloids isolated from each color morph was evaluated and compared.

Halocyntin and papillosin, two new antimicrobial peptides isolated from hemocytes of the solitary tunicate, Halocynthia papillosa

We report here the screening of five marine invertebrate species from two taxa (tunicates and echinoderms) for the presence of cationic antimicrobial peptides (AMP) in defence cells (hemocytes). Antimicrobial activities were detected only in the two tunicates Microcosmus sabatieri and Halocynthia papillosa. In addition, we report the isolation and characterization of two novel peptides from H. papillosa hemocytes. These molecules display antibacterial activity against Gram-positive and Gram-negative bacteria. Complete peptide characterization was obtained by a combination of Edman degradation and mass spectrometry. The mature molecules, named halocyntin and papillosin, comprise 26 and 34 amino acid residues, respectively. Their primary structure display no significant similarities with previously described AMP.

Antimitotic activity of methoxyconidiol, a meroterpene isolated from an ascidian

Methoxyconidiol is a meroterpene previously extracted from the ascidian Aplidium aff. densum [A. Simon-Levert, A. Arrault, N. Bontemps-Subielos, C. Canal, B. Banaigs. Meroterpenes from the ascidian Aplidium aff. densum, J. Nat. Prod. 68 (2005) 1412-1415]. In the present work we investigated its antimitotic effect on eukaryotic cells by using a bioassay based on the sea urchin early embryo. This bioassay has been successfully used to evaluate the efficacy of antiproliferative agents and to rapidly determine the affected cell cycle phase. We demonstrated that methoxyconidiol inhibits the cleavages of sea urchin Sphaerechinus granularis and Paracentrotus lividus fertilized eggs. This meroterpene disrupts M-phase progression and completely blocks cytokinesis without having any effect on DNA replication. The treatment severely disturbs the establishment of a mitotic spindle, most likely by affecting microtubule dynamics. Moreover, while the cell cycle regulatory kinase cyclin B/CDK1 is activated, cyclin B proteolysis is inhibited, impeding the output of M-phase. This characteristic cell cycle arrest induced by methoxyconidiol in sea urchin eggs emphasizes the interest for this drug as a putative antiproliferative agent for tumor cells.

Total structure and inhibition of tumor cell proliferation of laxaphycins

From a mixed assemblage of Lyngbya majuscula rich marine cyanobacteria, we isolated a series of cell growth inhibitory cyclic peptides. The structures of the two major components, laxaphycins A (1) and B (2), and of two minor peptides, laxaphycins B2 (3) and B3 (4), were determined by spectroscopic methods and degradative analysis. Absolute configurations of natural and nonproteinogenic amino acids were determined by a combination of hydrolysis, synthesis of noncommercial residues, chemical derivatization, and HPLC analysis. The organism producing the laxaphycins was identified as the cyanobacterium Anabaena torulosa. The antiproliferative activity of laxaphycins was investigated on a panel of solid and lymphoblastic cancer cells. Our results demonstrate that in contrast to laxaphycin A, laxaphycin B inhibits the proliferation of sensitive and resistant human cancer cell lines and that this activity is strongly increased in the presence of laxaphycin A. This effect appears to be due to an unusual biological synergism.

Temporal Variation in the Production of Four Secondary Metabolites in a Colonial Ascidian

The ecological and applied importance of ascidian secondary metabolites is well reported, but little is known about temporal variation in the production of these compounds. Here, we examined seasonal variation in the production of the four main pyridoacridine alkaloids (shermilamine B, kuanoniamine D, and their deacetylated forms) of the purple morph of the ascidian Cystodytes sp. Five replicate samples were taken monthly from July 2004 to February 2006, and analyzed by high-performance liquid chromatography. Our results showed a high degree of intercolony variability in secondary metabolite concentration and a lack of statistically significant seasonal variation in the production of the four compounds. Minimum values, however, were consistently recorded over the studied years in late summer, after the reproductive period. These minima may be attributable to sexual exhaustion and seasonally varying biotic interactions or abiotic parameters.

Meroterpenes from the ascidian Aplidium aff. densum

Chemical investigation of the ascidian Aplidium aff. densum collected at Masirah Island, Oman, has resulted in the isolation of five meroterpenes: two new ones, methoxyconidiol (1) and didehydroconicol (2), and three related, known compounds, 3-5. The structures of 1 and 2 were determined by a combination of mass spectrometry and one- and two-dimensional high-field NMR techniques. Their biological activities against bacteria and human lymphoblastic cell lines were evaluated.

Distribution of a new rosmarinic acid derivative in Eryngium alpinum L. and other Apiaceae

The roots of Eryngium alpinum L. (Apiaceae) demonstrated radical scavenging properties toward the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in a TLC autographic assay. Isolation of the bioactive compounds allowed the identification of R-(+)-3'-O-beta-D-glucopyranosyl rosmarinic acid, a new rosmarinic acid derivative. The quantitative determination of the antioxidant capacity of the compound by chemoluminescence demonstrated half the activity of R-(+)-rosmarinic acid. To find another source richer in this compound, a chemotaxonomic study was conducted. The higher content was found in the aerial parts of Sanicula europeae L., also belonging to the Saniculoideae subfamily. Although present in most of the Eryngium species, this compound was not detected in Imperatoria ostruthium L., Pimpinella peregrina L., and Levisticum officinalis L. species from the Apioideae subfamily and Hydrocotyle asiatica L. from the Hydrocotyloideae subfamily. The results indicate that the new derivative R-(+)-3'-O-beta-D-glucopyranosyl rosmarinic acid is a potential chemotaxonomic marker of the Saniculoideae subfamily.

Cytotoxic effect of Laxaphycins A and B on human lymphoblastic cells (CCRF-CEM) using digitised videomicrofluorometry

Laxaphycin A (laxa A) and Laxaphycin B (laxa B), cyclic peptides isolated from the terrestrial blue-green alga Anabaena laxa or the marine cyanobacterium Lyngbya majuscula have antifungal and cytotoxic activities. We used numerical videomicrofluorometry and a protocol of multiple labelling with Hoescht 33342 (nuclear DNA), Rhodamine 123 (mitochondria) and Nile Red (plasma membrane) to study the cytotoxicity of these substances in human lymphoblastic cells sensitive (CEM-WT) or resistant (CEM-VLB and CEM-VM1) to anticancer agents. The results indicate a low resistance index of 2 for CEM-VLB cells treated with laxa B or laxa A + lava B. For the three cell strains, following laxa B treatment, we observed an increase of a polyploid cell subpopulation that could result from the alteration of topoisomerase-II activity. On the contrary, the simultaneous treatment by laxa A and laxa B led to a decrease of that subpopulation with increasing laxa A doses. However, the effect of laxa A was less pronounced in the CEM-VM1 cells, which present a low intrinsic topoisomerase-II activity. For CEM-VLB cells, the higher doses needed can be attributed to their MDR resistance. Though we observed a synergistic effect between laxa B and laxa A (the latter is inactive by itself), these results indicate a different mode of action for laxa B and laxa A + laxa B. A more precise study of the mode of action of these compounds is warranted.

Larval sensory abilities and mechanisms of habitat selection of a coral reef fish during settlement

Sensory abilities and preferences exhibited by mobile larvae during their transition to juvenile habitats can establish spatial heterogeneity that drives subsequent species interactions and dynamics of populations. We conducted a series of laboratory and field experiments using coral reef fish larvae (Chromis viridis) to determine: ecological determinants of settlement choice (conspecifics vs. heterospecifics vs. coral substrates); sensory mechanisms (visual, acoustic/vibratory, olfactory) underlying settlement choice; and sensory abilities (effective detection distances of habitat) under field conditions. C. viridis larvae responded positively to visual, acoustic/vibratory, and olfactory cues expressed by conspecifics. Overall, larvae chose compartments of experimental arenas containing conspecifics in 75% of trials, and failed to show any significant directional responses to heterospecifics or coral substrates. In field trials, C. viridis larvae detected reefs containing conspecifics using visual and/or acoustic/vibratory cues at distances <75 cm; detection distances increased to <375 cm when olfactory capacity was present (particularly for reefs located up-current). We conducted high performance liquid chromatography (HPLC) analyses of seawater containing C. viridis juveniles and isolated high concentrations of several organic compounds. Subsequent laboratory trials demonstrated that C. viridis larvae responded positively to only one of these organic compounds. This compound was characterized by a weak polarity and was detected at 230 nm with a 31-min retention time in HPLC. Overall, our results suggest that fishes may use a range of sensory mechanisms effective over different spatial scales to detect and choose settlement sites, and species-specific cues may play a vital role in establishment of spatial patterns at settlement.

Culture of the marine cyanobacterium, Lyngbya majuscula (Oscillatoriaceae), for bioprocess intensified production of cyclic and linear lipopeptides

Cyanobacteria are an ancient and diverse group of photosynthetic microorganisms, which inhabit many different and extreme environments. This indicates a high degree of biological adaptation, which has enabled these organisms to thrive and compete effectively in nature. The filamentous cyanobacterium, Lyngbya majuscula, produces several promising antifungal and cytotoxic agents, including laxaphycin A and B and curacin A. Samples of L. majuscula collected from Moorea Island, Tahiti (French Polynesia) and from the Culture Collection of Algae and Protozoa (CCAP 1446/4) were studied and adapted to large scale laboratory culture (5 l). This constitutes a 100-fold scale-up for the culture of this particular strain of L. majuscula. The effect of culture vessel configurations, growth conditions and media compositions on growth of L. majuscula was examined. Using optimised culture conditions, two strains of L. majuscula are currently being evaluated for their production of secondary metabolites. Results will be compared with those obtained from four environmental extracts. Comparisons were made by thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). It was shown that varying the culture conditions under which L. majuscula was grown had the greatest effect on secondary metabolite production, thus providing potential for future bioprocess intensified production.

Structure-activity relationship for bromoindole carbaldehydes: effects on the sea urchin embryo cell cycle

Natural derivatives of indole-3-carbaldehyde were isolated from the tropical marine ascidian Stomoza murravi. A series of 13 derivatives, three natural and 10 synthetic (brominated and N-methylated), were examined for their effects on cell division of sea urchin eggs. These derivatives were shown to inhibit the first mitotic cycle in a concentration-dependent manner. By comparing the IC50 values with the structure of the various molecules, we were able to determine that bromination increased the cytotoxicity of the compound with a maximum occurring when bromine was added to carbon number 2, while addition of N-methylation was shown to markedly reduce the cytotoxicity of these same compounds brominated at carbon 2 only. Biological activity of this family of compounds has been characterized, via detailed study of addition of the most active derivative, 2,5,6-tribromoindole-3-carbaldehyde, on macromolecule synthesis and cytoskeleton reorganization during the first mitotic cycle of fertilized sea urchin eggs. Fluorescence localization of chromatin and microtubules revealed that 2,5,6-tribromoindole-3-carbaldehyde allowed pronuclei migration and fusion but prevented the condensation of chromatin, nuclear envelope breakdown, and bipolar mitotic spindle assembly, inducing an arrest of sea urchin embryogenesis at the beginning of mitosis. It is postulated here that this phenotype is likely to be due to a strong inhibition of DNA replication and protein synthesis.

Inhibition of topoisomerase II by the marine alkaloid ascididemin and induction of apoptosis in leukemia cells

Ascididemin (ASC) is a pentacyclic DNA-intercalating agent isolated from the Mediterranean ascidian Cystodytes dellechiajei. This marine alkaloid exhibits marked cytotoxic activities against a range of tumor cells, but its mechanism of action remains poorly understood. We investigated the effects of ASC on DNA cleavage by human topoisomerases I and II. Relaxation assays using supercoiled DNA showed that ASC stimulated double-stranded cleavage of DNA by topoisomerase II, but exerted only a very weak effect on topoisomerase I. ASC is a conventional topoisomerase II poison that significantly promoted DNA cleavage, essentially at sites having a C on the 3' side of the cleaved bond (-1 position), as observed with etoposide. The stimulation of DNA cleavage by topoisomerase I in the presence of ASC was considerably weaker than that observed with camptothecin. Cytotoxicity measurements showed that ASC was even less toxic to P388 leukemia cells than to P388CPT5 cells resistant to camptothecin. In addition, the marine alkaloid was found to be equally toxic to HL-60 leukemia cells sensitive or resistant to mitoxantrone. It is therefore unlikely that topoisomerases are the main cellular targets for ASC. This alkaloid was found to strongly induce apoptosis in HL-60 and P388 leukemia cells. Cell cycle analysis showed that ASC treatment was associated with a loss of cells in the G1 phase accompanied with a large increase in the sub-G1 region. Cleavage experiments with poly(ADP-ribose) polymerase (PARP) revealed that caspase-3 was a mediator of the apoptotic pathway induced by ASC. The DNA of ASC-treated cells was severely fragmented. Collectively, these findings indicate that ASC is a potent inducer of apoptosis in leukemia cells.

Matemone, a new bioactive bromine-containing oxindole alkaloid from the indian ocean sponge Iotrochota purpurea

A new bioactive bromine-containing oxindole alkaloid, matemone (1), was isolated from the Indian Ocean sponge Iotrochota purpurea, together with the known 6-bromoindole-3-carbaldehyde. The structures were elucidated on the basis of spectral and chemical data. Compound 1 shows mild cytotoxicity against three cancer cell lines and marginal antibacterial activity against Staphyloccocus aureus. DNA intercalant screening demonstrated DNA interactions with 1. Both compounds inhibit division of sea-urchin eggs.