De nouvelles voies d’inhibition des biofilms. Des micro-organismes producteurs de nouvelles molécules actives

Lors d’une immersion en eau de mer, tous les matériaux et structures sont rapidement colonisés par des salissures d’origine biologique : des biofilms. La transformation des propriétés de surface dumatériau et la présence demicro- oumacro-organismes (bactéries, algues, balanes, larves) engendrent des risques accrus de corrosion localisée, la biodétérioration desmatériaux immergés, le blocage des fonctions mécaniques…Afin de contrôler le dépôt et le développement de ces biofilms, la méthode privilégiée est l’application de peintures anti-salissures. Cependant ces revêtements sont généralement toxiques pour l’environnement. C’est pourquoi, les travaux menés actuellement visent à isoler de nouvelles molécules, produites par les bactéries marines, dans le but de développer des moyens de luttes écologiques et non toxiques contre les biofilms indésirables.

Allocation du carbone et métabolisme azoté chez l'haptophyte Tisochrysis lutea

The aim of this thesis is to improve knowledge on mechanisms involved in the response to nitrogen limitation and in lipid accumulation in the microalgae haptophyte Tisochrysis lutea. The wild type strain and a lipid accumulating mutant strain were grown under different nitrogen limitation and starvation and analyzed by functional genomics. Four genes of high-affinity nitrate/nitrite transporter (Nrt2) were identified and characterized to reveal the mechanisms involved in mineral absorption in this species. Transcriptomes of both strains were sequenced and proteins affected by nitrogen starvation and differentially expressed between the two strains were identified. We so identified the functions regulated by nitrogen deficiency and potentially involved in the accumulation of storage lipids. The responses of both strains to thin variations of nitrogen limitation were studied. The results of high-throughput proteomic analyzes suggest that the lipid-accumulation in the mutant strain is the result of carbon metabolism impacted overall, this spurred on signaling mechanisms. Two proteins have been studied since probably involved in carbon and nitrogen remobilization from amino acids catabolism during nitrogen limitation. This work increases knowledge on haptophytes, and brings assumptions on metabolic key involved in nitrogen limitation and carbon allocation in microalgae.

Analyse du compartiment mésozooplanctonique et écologie alimentaire printanière de la sardine, Sardina pilchardus (Walbaum, 1782), et de l’anchois, Engraulis encrasicolus (Linné, 1758) adultes dans le Golfe de Gascogne

Dietary studies of marine species constitute an important key to improve the understanding of its biology and of its role in the ecosystem. Thus, prey-predator relationships structure and determine population dynamics and the trophic network at the ecosystem scale. Among the major study sites, the marine ecosystem is submitted to natural and anthropogenic constraints. In the North-Eastern part of the Atlantic Ocean, the Bay of Biscay is a large open area surrounded South by Spain and East by France. This bay is an historic place of intense fishery activities for which the main small pelagic species targeted are the pilchard, Sardina pilchardus and the anchovy, Engraulis encrasicolus. The aim of this work is to analyze the trophic ecology of these two small pelagic fish in spring in the Bay of Biscay. To do this, a first section is devoted to their prey composed by the mesozooplanktonic compartment, through a two-fold approach: the characterization of their spatio-temporal dynamics during the decade 2003-2013 and the measurement of their energetic content in spring. For this season, it appears that all prey types are not worth energetically and that the Bay of Biscay represents a mosaic of dietary habitat. Moreover, the spring mesozooplankton community presents a strong spatial structuration, a temporal evolution marked by a major change in abundance and a control by the microphytoplankton biomass. The second section of this work is relative to a methodological approach of the trophic ecology of S. pilchardus and E. encrasicolus. Three different trophic tracers have been used: isotopic ratios of carbon and nitrogen, parasitological fauna and mercury contamination levels. To improve the use of the first of these trophic tracers, an experimental approach has been conducted with S. pilchardus to determine a trophic discrimination factor. Finally, it appears that the use of these three trophic tracers has always been permitted to highlight a temporal variability of the relative trophic ecology of these fish. However, no spatial dynamics could be identified through these three trophic tracers.