La BMAA (ƒÀ-N-methylamino-L-alanine) est un acide amine non proteique neurotoxique associe a la sclerose laterale amyotrophique dont la detection souffre d'une controverse analytique remettant en question sa production par l'ensemble des cyanobacteries. Notre premier objectif etait donc de developper une methode d'analyse de la BMAA et ses isomeres, tres selective, par chromatographie HILIC couplee a la spectrometrie de masse. Nous avons ensuite cultive et crible une cinquantaine d'especes de microalgues (e.g. cyanobacteries, diatomees). Contrairement au DAB, un isomere largement retrouve, la BMAA a ete decouverte seulement dans 5 souches de diatomees, remettant en question sa qualification de cyanotoxine. En parallele, nous avons evalue la presence de BMAA sur les cotes francaises. Elle a ete detectee dans differents compartiments de l'ecosysteme de Thau (i.e. plancton, biofilm et moule) nous amenant a emettre l'hypothese d'une bioaccumulation, avec les diatomees comme source de BMAA. De plus, tous les mollusques collectes mensuellement dans 10 zones conchylicoles en 2013 contiennent la BMAA et ses isomeres, suggerant qu'ils sont continuellement presents dans les bivalves alors que le mecanisme de bioaccumulation n'est pas connu. Une premiere experience de contamination au laboratoire revele un possible lien, a confirmer, entre l'accumulation de BMAA dans les moules et leur consommation d'une diatomee productrice de BMAA. Enfin, la procedure d'analyse multi-cyanotoxines developpee a permis la detection de cylindrospermopsine dans le biofilms de coquillages de Thau, suggerant l'interet de poursuivre les travaux quant a la problematique cyanotoxines dans l'environnement marin.

BMAA (â-N-methylamino-L-alanine) is a non proteinogenic neurotoxic amino acid that has been associated with amyotrophic lateral sclerosis. Its analytical detection is widely debated thus the global production of BMAA by cyanobacteria is questioned. We first aimed at developing an analytical method allowing for highly selective identification of BMAA and isomers, using HILIC chromatography coupled to mass spectrometry. Then, we have cultivated and analyzed more than 50 microalgae (e.g. cyanobacteria, diatoms). Unlike DAB, one of its natural isomer, BMAA was only reported in five diatom species and cannot be accounted as a cyanotoxin anymore. In parallel, we have evaluated the presence of BMAA on the three French coasts. The presence of BMAA in different compartments of the Thau lagoon food web (i.e. plankton, biofilm and mussel) led us to hypothesize a bioaccumulation pathway with diatom as a source of BMAA. Moreover, BMAA and DAB were both detected in all mollusk samples collected once a month in 2013 from 10 French shellfish production areas. While they were continuously detected, the bioaccumulation mechanism of these amino acids is unknown. Therefore, we tried to contaminate blue mussels in controlled conditions with a BMAA-producing diatom. Results of this first attempt may suggest a link between the accumulation of BMAA in mussel and their consumption of the diatom strain. Finally, the multi-cyanotoxins analytical procedure that we developed allowed us to detect cylindrospermopsin in biofilms collected from mussels of Thau lagoon, calling for extended research efforts on cyanotoxins-derived issue in the marine environment.