Jean-Luc Mouget

Key features of intertidal food webs that support migratory shorebirds.

The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Oléron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain – Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds.

Antimicrobial Compounds from Eukaryotic Microalgae against Human Pathogens and Diseases in Aquaculture

The search for novel compounds of marine origin has increased in the last decades for their application in various areas such as pharmaceutical, human or animal nutrition, cosmetics or bioenergy. In this context of blue technology development, microalgae are of particular interest due to their immense biodiversity and their relatively simple growth needs. In this review, we discuss about the promising use of microalgae and microalgal compounds as sources of natural antibiotics against human pathogens but also about their potential to limit microbial infections in aquaculture. An alternative to conventional antibiotics is needed as the microbial resistance to these drugs is increasing in humans and animals. Furthermore, using natural antibiotics for livestock could meet the consumer demand to avoid chemicals in food, would support a sustainable aquaculture and present the advantage of being environmentally friendly. Using natural and renewable microalgal compounds is still in its early days, but considering the important research development and rapid improvement in culture, extraction and purification processes, the valorization of microalgae will surely extend in the future.

Bacterial adhesion and growth reduction by novel rubber-derived oligomers

In the medical field, attached bacteria can cause infections associated with catheters, incisions, burns, and medical implants especially in immunocompromised patients. The problem is exacerbated by the fact that attached bacteria are ∼1000 times more resistant to antibiotics than planktonic cells. The rapid spread of antibiotic resistance in these and other organisms has led to a significant need to find new methods for preventing bacterial attachment. The goal of this research was to evaluate the effectiveness of novel polymer coatings to prevent the attachment of three medically relevant bacteria. Tests were conducted with Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus for oligomers derived from modifications of natural rubber (cis 1,4-polyisoprene). The different oligomers were: PP04, with no quaternary ammonium (QA); MV067, one QA; PP06, three QA groups. In almost all experiments, cell attachment was inhibited to various extents as long as the oligomers were used. PP06 was the most effective as it decreased the planktonic cell numbers by at least 50% for all bacteria. Differences between species sensitivity were also observed. P. aeruginosa was the most resistant bacteria tested, S. aureus, the most sensitive. Further experiments are required to understand the full extent and mode of the antimicrobial properties of these surfaces.

A new blue-pigmented hasleoid diatom, Haslea provincialis, from the Mediterranean Sea

Abstract Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been repeatedly observed and resulted in viable initial cells. There were no sexual interactions with sexually competent clones of H. ostrearia or H. karadagensis, as would be expected for a separate biological species. There are strong similarities between the H. provincialis pigment and the marennine produced by H. ostrearia, evidenced by UV-visible spectrophotometry and Raman spectrometry. However, unlike the marennine from H. ostrearia, no differences were found between the extracellular and the intracellular forms of the pigment in H. provincialis. This indicates that the synthesis pathways and excretion mechanisms among the three ‘blue’ Haslea may be species-specific. Molecular taxonomy and phylogeny (based on rbcL, cox1 and SSU V4 DNA sequences) confirmed the distinct position of this species among the blue Haslea species. Haslea provincialis occurs in environments from which H. ostrearia has already been reported (mostly based on the presence of the blue cell vacuoles). Possible species misidentifications and the impact of the complex geological history of the Mediterranean Sea on blue diatom diversification are also discussed.

Time-dependent upregulation of electron transport with concomitant induction of regulated excitation dissipation in Haslea diatoms

Photoacclimation by strains of Haslea “blue” diatom species H. ostrearia and H. silbo sp. nov. ined. was investigated with rapid light curves and induction–recovery curves using fast repetition rate fluorescence. Cultures were grown to exponential phase under 50xa0µmolxa0m−2xa0s−1 photosynthetic available radiation (PAR) and then exposed to non-sequential rapid light curves where, once electron transport rate (ETR) had reached saturation, light intensity was decreased and then further increased prior to returning to near growth light intensity. The non-sequential rapid light curve revealed that ETR was not proportional to the instantaneously applied light intensity, due to rapid photoacclimation. Changes in the effective absorption cross sections for open PSII reaction centres (σPSII′) or reaction centre connectivity (ρ) did not account for the observed increases in ETR under extended high light. σPSII′ in fact decreased as a function of a time-dependent induction of regulated excitation dissipation Y(NPQ), once cells were at or above a PAR coinciding with saturation of ETR. Instead, the observed increases in ETR under extended high light were explained by an increase in the rate of PSII reopening, i.e. QA− oxidation. This acceleration of electron transport was strictly light dependent and relaxed within seconds after a return to low light or darkness. The time-dependent nature of ETR upregulation and regulated NPQ induction was verified using induction–recovery curves. Our findings show a time-dependent induction of excitation dissipation, in parallel with very rapid photoacclimation of electron transport, which combine to make ETR independent of short-term changes in PAR. This supports a selective advantage for these diatoms when exposed to fluctuating light in their environment.

Antioxidant activity of three microalgae Dunaliella salina, Tetraselmis chuii and Isochrysis galbana clone Tahiti

Natural alternatives antioxidant source has become a trending topic in the past decades to replace synthetic antioxidant. Microalgae have been mentioned to show interesting bioactive properties and one of them is its antioxidant activity. This study aims to evaluate the potential of three microalgae Dunaliella salina, Tetraselmis chuii and Isochrysis galbanaas new source of natural antioxidant. Proximate analysis and total phenolic content of D. salina, T. chuii and I. galbanas were determined. Antioxidant activity of methanolic extracts of these three species prepared in different concentration (50, 100, 250, 500, and 1000 ppm) was performed through DPPH assay. I. galbana clone Tahiti demonstrated a highest antioxidant potential with 61.64 of inhibition at 50 ppm followed by D. salina with 58.45 % of inhibition and T. chuii with 52.58 % of inhibition. I. galbana clone Tahiti was the best antioxidant with total phenol content of 17.798 mg GAE g-1 extract at 50 ppm; followed by T. chuii 16.868 mg GAE g-1 extract and the lowest was D. salina with 4.672 mg GAE g-1 extract. Results suggest that these microalgae posses antioxidant potential which could be considered for future applications in medicine, dietary supplements, cosmetics or food industries.

Anticancer, Antiviral, Antibacterial, and Antifungal Properties in Microalgae

Abstract Microalgae and cyanobacteria are photoautotrophic microorganisms, present in almost all ecosystems around the world. Due to their rich biodiversity and possibly high growth performances, microalgae are the basis of most aquatic ecosystems; however, they constitute a vast bioresource, underexplored and underexploited yet. Regarding health and disease prevention, microalgae and cyanobacteria have been recognized as potential sources of new natural antimicrobial substances. Indeed, these organisms produce a great variety of bioactive secondary metabolites, which are accumulated in the cell or excreted in the surrounding environments, usually at the end of the exponential and the stationary phase of growth. Many of these metabolites display antibacterial activity, such as free saturated or unsaturated fatty acids, and there is a research effort to find natural molecules to allow limiting the misuse of commercial antibiotics, because their prolonged use may result in the development of resistant bacterial strains. Other microalgal and cyanobacterial compounds present antiproliferative or antifungal properties, or are able to inhibit viral infection and/or replication. One major potential but promising commercial application of these substances is thus the area of pharmaceuticals, antibiotics, and other biologically active compounds.

Mitogenome sequence of a Black Sea isolate of the kinetoplastid Bodo saltans

Abstract We obtained the mitogenome sequence of a Black Sea isolate of the kinetoplastid Bodo saltans. This sequence consists of two contigs totaling 24,925u2009bp and encodes ten protein-coding genes, one conserved ORF and one rRNA gene. Alignment of the Black Sea mitogenome with the limited sequence data currently available in public databases for another strain of B. saltans revealed significant genetic divergence between the two isolates. Maximum likelihood phylogenetic inference clearly resolved the Bodonidae from the Trypanosomatidae.

The complete mitochondrial DNA of the tropical oyster Crassostrea belcheri from the Cần Giò’ mangrove in Vietnam

Abstract The complete mitochondrial genome of the oyster Crassostrea belcheri from the Cần Giò’ mangrove in Vietnam has been sequenced. It consists of a circular DNA molecule of 21020 base pairs (bp), coding for 12 proteins, 20 transfer RNAs, and two ribosomal RNAs. Like the mitogenomes of Crassostrea iredalei and Crassostrea sp. DB1, it contains a non-coding region and two ORFs. The C. belcheri mitogenome provides information that could improve the molecular phylogeny of Asian oysters and be useful to the development of oyster aquaculture in South East Asia.

Cell size-based, passive selection of the blue diatom Haslea ostrearia by the oyster Crassostrea gigas

Pre-ingestive selection has been identified as a feeding mechanism of oysters that may influence their uptake of particles and microalgal cells. Oysters can feed specifically on the pennate diatom Haslea ostrearia, which produces the blue pigment marennine that is responsible for the greening of oysters. Because the size of particles or cells plays a significant role in the selection process, and given that diatoms experience a decrease in size as a consequence of vegetative reproduction, H. ostrearia consumption and marennine uptake might be influenced by pre-ingestive selection. We examined the role of H. ostrearia cell size in the selective feeding of Crassostrea gigas. Individual flow-through chambers were used to deliver mixtures of H. ostrearia of varying cell length to oysters. Inflow, outflow and pseudofaecal samples were collected from chambers during oyster feeding. Video-endoscopy was used to sample material in the dorsal and ventral particle tracts. Diatom cells counts showed that pseudofaeces contained on average larger cells than the ambient medium. However, proportions of the different populations of H. ostrearia in pseudofaeces were identical to those in the ventral tracts, indicating that no selection was performed by the labial palps. Video-endoscopy, plus imaging by scanning electron microscopy, of gills and labial palps revealed that only those larger H. ostrearia that were orientated dorsoventrally could enter the principal filaments (pfs) and then access the dorsal acceptance tract. These results show that for particles like Haslea cells with only one axis exceeding the width of the pfs, the selection on the oyster gills is passive and based on cell size.