Mécanismes de précipitation de carbonate de calcium dans les biofilms photosynthétiques

La précipitation de carbonate de calcium dans les systèmes benthiques est souvent associée aux biofilms photosynthétiques, et notamment observée au sein de structures d'une grande complexité morphologique comme les tapis microbiens, les stromatolithes et les microbialithes. Cette biocalcification modifie les flux de CO2, de calcium et d'alcalinité dans les hydrosystèmes (séquestration du carbone inorganique et d'alcalinité). Ce processus paraît donc très sensible aux impacts anthropiques, e.g. la perturbation globale du cycle du carbone et les contaminations atmosphériques. Son étude revêt une importance capitale pour la compréhension des paléoenvironnements. Différentes hypothèses ont été avancées pour expliquer la biocalcification dans ces biofilms. L'activité photosynthétique des cyanobactéries est souvent mise en cause, mais ce mécanisme est parfois contesté, privilégiant l'activité métabolique des bactéries organohétérotrophes, e.g. les bactéries sulfato-réductrices, qui sont associées aux micro-organismes phototrophes dans les biofilms La calcification peut aussi être contrôlée directement par l'interaction du calcium avec la matière organique, notamment les polymères extracellulaires sécrétés par les microorganismes (EPS) ou les fractions macromoléculaires riches en acides aspartique et glutamique de la matière organique dissoute (MOD)

Resting Cyst Distribution and Molecular Identification of the Harmful Dinoflagellate Margalefidinium polykrikoides (Gymnodiniales, Dinophyceae) in Lampung Bay, Sumatra, Indonesia

Margalefidinium polykrikoides, an unarmored dinoflagellate, was suspected to be the causative agent of the harmful algal blooms – associated with massive fish mortalities – that have occurred continually in Lampung Bay, Indonesia, since the first bloom event in October 2012. In this study, after examination of the morphology of putative M. polykrikoides-like cysts sampled in bottom sediments, cyst bed distribution of this harmful species was explored in the inner bay. Sediment samples showed that resting cysts, including several morphotypes previously reported as M. polykrikoides, were most abundant on the northern coast of Lampung Bay, ranging from 20.6 to 645.6 cysts g-1 dry sediment. Molecular phylogeny inferred from LSU rDNA revealed that the so-called Mediterranean ribotype was detected in the sediment while M. polykrikoides motile cells, four-cell chain forming in bloom conditions, belonged to the American-Malaysian ribotype. Moreover, hyaline cysts, exclusively in the form of four-cell chains, were also recorded. Overall, these results unequivocally show that the species M. polykrikoides is abundantly present, in the form of vegetative cells, hyaline and resting cysts in an Indonesian area

The globally distributed genus Alexandrium: Multifaceted roles in marine ecosystems and impacts on human health

The dinoflagellate genus Alexandrium is one of the major harmful algal bloom (HAB) genera with respect to the diversity, magnitude and consequences of blooms. The ability of Alexandrium to colonize multiple habitats and to persist over large regions through time is testimony to the adaptability and resilience of this group of species. Three different families of toxins, as well as an as yet incompletely characterized suite of allelochemicals are produced among Alexandrium species. Nutritional strategies are equally diverse, including the ability to utilize a range of inorganic and organic nutrient sources, and feeding by ingestion of other organisms. Many Alexandrium species have complex life histories that include sexuality and often, but not always, cyst formation, which is characteristic of a meroplanktonic life strategy and offers considerable ecological advantages. Due to the public health and ecosystem impacts of Alexandrium blooms, the genus has been extensively studied, and there exists a broad knowledge base that ranges from taxonomy and phylogeny through genomics and toxin biosynthesis to bloom dynamics and modeling. Here we present a review of the genus Alexandrium, focusing on the major toxic and otherwise harmful species

In silico prediction of the secretome from the invasive neurotoxic marine dinoflagellate Alexandrium catenella

WOS:000474226700010Alexandrium catenella, a marine dinoflagellate responsible for harmful algal blooms (HABs), proliferates with greater frequency, distribution and intensity, in disturbed marine coastal ecosystems. The proteins secreted into seawater may play a crucial role in maintaining this dinoflagellate in these ecosystems, but this possibility has never been investigated before. In this study, the A. catenella secretome was predicted from its transcriptome by combining several bioinformatics tools. Our results predict a secretome of 2 779 proteins, among which 79% contain less than 500 amino acids, suggesting that most secreted proteins are short in length. The predicted secretome includes 963 proteins (35%) with Pfam domains: 773 proteins with one Pfam domain and 190 proteins with two or more Pfam domains. Their functional annotation showed that they are mainly involved in (i) proteolysis, (ii) stress responses and (iii) primary metabolism. In addition, 47% of the secreted proteins appear to be enzymes, primarily peptidases, known to be biologically active in the extracellular medium during stress responses. Finally, this study provides a wealth of candidates of proteins secreted by A. catenella, which may interact with the marine environment and help this dinoflagellate develop in various environmental conditions

Modifications of the soluble proteome of a mediterranean strain of the invasive neurotoxic dinoflagellate Alexandrium catenella under metal stress conditions

International audienceThe soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18 μM (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P < 0.05) the total number of protein spots (−41%, −52% and −60%, at 6, 12 or 18 μM, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20–37% for lead; 36–50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP+ reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29–34% for lead; 17–36% for zinc) (superoxide dismutase: SOD; proteasome α/β subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase β subunit (+16.3 fold after exposure to lead at 12 μM). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems

Geographic structure evidenced in the toxic dinoflagellate Alexandrium pacificum Litaker (A. catenella - group IV (Whedon & Kofoid) Balech) along Japanese and Chinese coastal waters

The intra-specific diversity and genetic structure within the Alexandrium pacificum Litaker (A. catenella - Group IV) populations along the Temperate Asian coasts, were studied among individuals isolated from Japan to China. The UPGMA dendrogram and FCA revealed the existence of 3 clusters. Assignment analysis suggested the occurrence of gene flows between the Japanese Pacific coast (cluster-1) and the Chinese Zhejiang coast (cluster-2). Human transportations are suspected to explain the lack of genetic difference between several pairs of distant Japanese samples, hardly explained by a natural dispersal mechanism. The genetic isolation of the population established in the Sea of Japan (cluster-3) suggested the existence of a strong ecological and geographical barrier. Along the Pacific coasts, the South North current allows limited exchanges between Chinese and Japanese populations. The relationships between Temperate Asian and Mediterranean individuals suggested different scenario of large-scale dispersal mechanisms

Distribution and abundance of Pyrodinium bahamense cyst in the harmful algal blooms risk waters in Indonesia

Number: 1International audienceDistribution and abundance of Pyrodinium bahamense cyst in the harmful algal blooms risk waters in Indonesia. Pyrodinium bahamenseas Harmful Algal Blooms (HABs) is one of the rising environmental problems in the coastal areas of Southeast Asia, particularly in Indonesia. Cyst bank formed after the blooms of P. bahamense is a potential source for the future blooming events. Therefore, an effort to describe the distribution and abundance of P. bahamense cyst banks in Indonesian coastal waters is necessary as a part of the mitigation strategy against the negative impacts of those toxic dinoflagellate blooms. This study was done as a desk study, which included a literature study, reanalysed of previous research data, and reanalysed of preserved samples or stored raw samples. Data and samples used in this study were collected and analysed from part of past researches in Lampung Bay, Jakarta Bay, Cirebon coastal waters, and Ambon Bay. This study also included an analysis to determine the P. Bahamense HABs risk level in the studied areas based on the cyst density and distribution data. Results showed a low density of P. bahamense cyst in Lampung Bay and Jakarta Bay, with cyst density \textless50 cysts.g-1 wet sediment. In contrast, the bottom sediments of Ambon Bay and Cirebon coastal waters contained high cyst density, which reached \textgreater1,000 cysts.g-1 wet sediment. Based on those data, the P. Bahamense HABs risk in Jakarta Bay and Lampung Bay would be generally much lower compared to Ambon Bay and Cirebon waters. The existence of cyst banks in those coastal waters may indicate  a possibility of future blooms of P. bahamense

Intraspecific variability in membrane proteome, cell growth, and morphometry of the invasive marine neurotoxic dinoflagellate Alexandrium pacificum grown in metal-contaminated conditions

International audienceOver the past decades, the occurrence, distribution and intensity of harmful algal blooms involving the dinofla-gellate Alexandrium pacificum have increased in marine coastal areas disturbed by anthropogenic inputs. This in-vasive species produces saxitoxin, which causes the paralytic shellfish poisoning syndrome in humans upon consumption of contaminated seafood. Blooms of A. pacificum have been reported in metal-contaminated coastal ecosystems, suggesting some ability of these microorganisms to adapt to and/or resist in metal stress conditions. This study seeks to characterize the modifications in membrane proteomes (by 2-D electrophoresis coupled to LC-MS/MS), cell growth and morphometry (measured with an inverted microscope), in response to metal stress (addition of Zn2+,Pb2+,Cu2+ and Cd2+), in two Mediterranean A pacOcum strains: SG C10-3 and TAR C5-4F, re-spectively isolated from the Santa Giusta Lagoon (Sardinia, Italy) and from the Tarragona seaport (Spain), both metal-contaminated ecosystems. In the SG C10-3 cultures grown in a metal cocktail, cell growth was significantly delayed, and cell size increased (22% of 37.5 mu m cells after 25 days of growth). Conversely, no substantial change was observed for cell growth or cell size in the TAR C5-4F cultures grown in a metal cocktail (P> 0.10), thus in-dicating intraspecific variability in the responses of A. pacificum strains to metal contamination. Regardless of the conditions tested, the total number of proteins constituting the membrane proteome was significantly higher for TAR C5-4F than for SG C10-3, which may help TAR C5-4F to thrive better in contaminated conditions. For both strains, the total number of proteins constituting the membrane proteomes was significantly lower in response to metal stress (29% decrease in the SG C10-3 proteome: 82 +/- 12 proteins for controls, and 58 +/- 12 in metalcontaminated cultures; 17% decrease in the TAR C5-4F proteome: 101 +/- 8 proteins for controls, and 84 +/- 5 in metal-contaminated cultures). Moreover, regardless of the strain, proteins with significantly modified expression in response to stress were mainly down-regulated (representing 45% of the proteome for SG C10-3 and 38% for TAR C5-4F), dearly showing the harmful effects of the metals. Protein down-regulation may affect cell transport (actin and phospholipid scramblase in SG C10-3), photosynthesis (RUBISCO in SG C10-3, light-harvesting protein in TAR C5-4F, and high-CO2-inducing periplasmic protein in both strains), and finally energy metabolism (ATP synthase in both strains). However, other modifications in protein expression may confer to these A. pacificum strains a capacity for adaptation and/or resistance to metal stress conditions, for example by (i) limiting the metal entry through the plasma membrane of the SG C10-3 cells (via the down-regulation of scramblase) and/or (ii) reducing the oxidative stress generated by metals in SG C10-3 and TAR C5-4F cells (due to down-regulation of ATP-synthase)

Metal stresses modify soluble proteomes and toxin profiles in two Mediterranean strains of the distributed dinoflagellate Alexandrium pacificum

WOS:000789651000009HABs involving Alexandrium pacificum have been reported in metal-contaminated ecosystems, suggesting that this distributed species adapts to and/or can tolerate the effects of metals. Modifications in soluble proteomes and PST contents were characterized in two Mediterranean A. pacificum strains exposed to mono- or polymetallic stresses (zinc, lead, copper, cadmium). These strains were isolated from two anthropized locations: Santa Giusta Lagoon (Italy, SG C10-3) and the Tarragona seaport (Spain, TAR C5-4F). In both strains, metals primarily downregulated key photosynthesis proteins. Metals also upregulated other proteins involved in photosynthesis (PCP in both strains), the oxidative stress response (HSP 60, proteasome and SOD in SG C10-3; HSP 70 in TAR C5-4F), energy metabolism (AdK in TAR C5-4F), neoglucogenesis/glycolysis (GAPDH and PEP synthase in SG C10-3) and protein modification (PP in TAR C5-4F). These proteins, possibly involved in adaptive proteomic responses, may explain the development of these A. pacificum strains in metal-contaminated ecosystems. The two strains showed different proteomic responses to metals, with SG C10-3 upregulating more proteins, particularly PCP. Among the PSTs, regardless of the metal and the strain studied, C2 and GTX4 predominated, followed by GTX5. Under the polymetallic cocktail, (i) total PSTs, C2 and GTX4 reached the highest levels in SG C10-3 only, and (ii) total PSTs, C2, GTX5 and neoSTX were higher in SG C10-3 than in TAR C5-4F, whereas in SG C10-3 under copper stress, total PSTs, GTX5, GTX1 and C1 were higher than in the controls, revealing variability in PST biosynthesis between the two strains. Total PSTs, C2, GTX4 and GTX1 showed significant positive correlations with PCP, indicating that PST production may be positively related to photosynthesis. Our results showed that the A. pacificum strains adapt their proteomic and physiological responses to metals, which may contribute to their ecological success in highly anthropized areas

Beta-N-methylamino-L-alanine (BMAA) and isomers : distribution in different food web compartments of Thau lagoon, French Mediterranean Sea

The neurotoxin BMAA (beta-N-methylamino-L-alanine) and its isomer DAB (2,4-diaminobutyric acid) have been detected in seafood worldwide, including in Thau lagoon (French Mediterranean Sea). A cluster of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease associated with BMAA, has also been observed in this region. Mussels, periphyton (i.e. biofilms attached to mussels) and plankton were sampled between July 2013 and October 2014, and analyzed using HILIC-MS/MS. BMAA, DAB and AEG (N-(2-aminoethyl)glycine) were found in almost all the samples of the lagoon. BMAA and DAB were present at 0.58 and 0.83, 2.6 and 33, 4.0 and 7.2 mu g g(-1) dry weight in plankton collected with nets, periphyton and mussels, respectively. Synechococcus sp., Ostreococcus tauri, Alexandrium catenella and eight species of diatoms were cultured and screened for BMAA and analogs. While Synechococcus sp., O. tauri and A. catenella did not produce BMAA under our culture conditions, four diatoms species contained both BMAA and DAB. Hence, diatoms may be a source of BMAA for mussels. Unlike other toxins produced by microalgae, BMAA and DAB were detected in significant amounts in tissues other than digestive glands in mussels