Jean-Rene Le Coz

Incorporation of Microalgae Sterols by Scallop Pecten maximus (L.) Larvae

Changes in sterol composition of Pecten maximus larvae during the larval development stage with standard algal mixtures and unialgal diets were analysed. The sterol composition of four microalgae currently used in mollusc hatchery were also examined. Under standard algal conditions, the larvae quickly use the steryl ester from larvae reserves during the endotrophic and the mixotrophe phases. The preferential incorporation of Pavlova lutheri and T-Isochrysis sterols, rather than Skeletonema costatum sterols, during the larval development stage would indicate that S. costatum cells were poorly ingested and digested by larvae. Among the ingested sterols, cholesterol and stigmasterol were preferentially incorporated by the larvae. Conversely, the larvae appeared able to limit the incorporation of methylpavlovol, ethylpavlovol, and 4alpha-methylporiferasterol. In the unialgal experiment, the best growths were obtained with the diet richest in cholesterol (Chaetoceros calcitrans) and the best compromise of good growth and settlement rate was observed with the diet richest in C24 ethyl sterol. The selective incorporation of the cholesterol was confirmed by the larval rearing with C. calcitrans. The strong sterol dietary imprint in larvae corroborated the absence of an important capacity in P. maximus larvae to convert or biosynthesise sterol.

Enhancement of neutral lipid productivity in the microalga Isochrysis affinis Galbana (T‐Iso) by a mutation‐selection procedure

Microalgae offer a high potential for energetic lipid storage as well as high growth rates. They are therefore considered promising candidates for biofuel production, with the selection of high lipid‐producing strains a major objective in projects on the development of this technology. We developed a mutation‐selection method aimed at increasing microalgae neutral lipid productivity. A two step method, based on UVc irradiation followed by flow cytometry selection, was applied to a set of strains that had an initial high lipid content and improvement was assessed by means of Nile‐red fluorescence measurements. The method was first tested on Isochrysis affinis galbana (T‐Iso). Following a first round of mutation‐selection, the total fatty acid content had not increased significantly, being

C/N ET CONTROLE DE LA PHYSIOLOGIE DES CULTURES DE PHYTOPLANCTON

262\pm 21\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}}

ECOPHYSIOLOGICAL AND METABOLIC ADAPTATIONS TO SULPHIDE EXPOSURE OF THE OYSTER CRASSOSTREA GIGAS

for the wild type (WT) and

Amélioration des productions phytoplanctoniques en écloserie de mollusques : caractérisation des microalgues fourrage

269\pm 49\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}}

Sterol production and phytosterol bioconversion in two species of heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans

for the selected population (S1M1). Conversely, fatty acid distribution among the lipid classes was affected by the process, resulting in a 20% increase for the fatty acids in the neutral lipids and a 40% decrease in the phospholipids. After a second mutation‐selection step (S2M2), the total fatty acid content reached

Oyster adenylate energy charge: response to levels of food

409\pm 64\,{\rm mgTFA}\,{\rm (gC)}^{- {\rm 1}}

Effect of sediment nearness on the metabolic enzyme activity and energy state of the oyster Crassostrea gigas

with a fatty acid distribution similar to the S1M1 population. Growth rate remained unaffected by the process, resulting in a 80% increase for neutral lipid productivity. Biotechnol. Bioeng. 2012; 109: 2737–2745.

Signification biologique des teneurs protéiques et des activités de l'amylase et des protéases chez Artemia salina L. aspects d'application a l'étude de la nutrition *

ABSTRACT Nutrients can be used for induction of carbohydrate or protein metabolism of three unicellular algae, their chemical variations measured by C/N ratio. The C/N determination and evolution can be used as a control for growth phase and satured conditions. Cultures of routine production have been tested by such a method. The results are discussed.

Effet de la qualité de l'eau sur la croissance larvaire de Pecten maximus en écloserie : observations préliminaires

Abstract The purpose of this study is to examine the response of the oyster Crassostrea gigas to sulphide at different biological scales. A first experiment was designed to measure for 20 h the clearance (CR) and oxygen consumption (OC) rates of oysters exposed at different concentrations of sulphide (0, 3, 6, 12, 20, and 40 μM). The second experiment was carried out to evaluate the metabolic adaptations to chronic sulphide exposure for 10 days by measuring PK and PEPCK enzyme activities, succinate and alanine content, the adenylate energy charge (AEC), and the activity of the electron transport system (ETS) in whole oysters at above 20 μM. PK and PEPCK mRNAs and enzyme activities have been measured in adductor muscle. When exposed to sulphide above 20 μM, CR stopped, whereas oyster maintained their average OC rate between 1 and 2 mg O2 h−1 g−1 dw. In the second experiment, sulphide exposure of oysters resulted in higher mortality, reduced the glycolytic flux by inhibiting the PK activity and decreased the ETS activity leading to a lower AEC. At day 10, a kind of recovery took place: the ETS activity and AEC of oysters exposed to sulphide increased to the level of the control oysters. In the adductor muscle, sulphide did not affect the transcriptional level of PK; PK was only regulated at enzyme level. Conversely, PEPCK was regulated only at transcriptional level. Nevertheless, muscle exhibited a wholly anaerobic metabolism by the significant increase of alanine and succinate contents followed by the significantly decrease of the ATP content during the 10 days of the experiment. This experiment showed that sulphide involved partially the whole oyster and wholly the adductor muscle in an anaerobic pathway of energy production; but oxygen was needed for the detoxification of the organism.