Sterol biosynthesis and phytosterol bioconversion in Crassostrea gigas larvae: new evidence from mass-balance feeding studies.

Fiz da Costa, Margaux Mathieu-Resuge, Fabienne Le Grand, Claudie Quéré, Gabriel V Markov, Gary H Wikfors, Philippe Soudant
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Abstract

Dietary sterols are important for bivalve larval growth and survival. The aim of the study was to determine quantitatively sterol incorporation and synthesis in Pacific oyster Crassostrea gigas larvae by means of a mass-balance approach. The flow-through larval rearing technique allowed accurate quantification of microalgal ingestion and consequently of sterol ingestion. Sterol incorporation was calculated using the sterol composition of the larvae between 2 sample points. Two sets of experiments were done using two cultured microalgae: Tisochrysis lutea (T) and Chaetoceros neogracile (Cg) as mono- and bi-specific diets (TCg). Accumulation of tissue sterols in oyster larvae, in addition to those present in the diet, indicate that C. gigas larvae appear to have the ability to synthetize sterols de novo under low dietary sterol supply, e.g., when fed the T diet. Sterol synthesis was dependent upon sterol dietary supply; larvae fed T exhibited greater sterol incorporation at the pediveliger stage than larvae fed TCg. Larval sterol compositions under the different dietary regimes indicate likely bioconversion pathways modifying dietary sterols. Larvae fed T bioconverted dietary brassicasterol mainly to cholesterol via a 22-dehydrocholesterol intermediate. Brassicasterol was also actively synthetized in larvae fed T and TCg, suggesting a possible metabolic role of this sterol in C. gigas larvae. Apparent desmosterol synthesis under all experimental conditions suggests a role as a membrane component or as an intermediate in cholesterol synthesis. Our data also indicate that C. gigas larvae require approximately 13 ng cholesterol larvae-1 to achieve competence for metamorphosis. This mass-balance approach will allow the determination of other biochemical requirements in larval nutrition.

长牡蛎幼虫的甾醇生物合成和植物甾醇生物转化:来自质量平衡摄食研究的新证据。
膳食固醇对双壳类幼虫的生长和存活很重要。本研究的目的是用质量平衡法定量测定太平洋牡蛎长牡蛎幼虫体内甾醇的掺入和合成。通过幼虫饲养技术可以精确量化微藻的摄取量,从而也可以量化甾醇的摄取量。利用2个采样点之间幼虫的甾醇组成计算甾醇掺入量。本试验采用两种培养的微藻:黄体溶藻(T)和新细毛藻(Cg)作为单特异性和双特异性饲料(TCg)。除了饲料中存在的组织固醇外,牡蛎幼虫体内组织固醇的积累表明,在低饲料固醇供应的情况下,如饲喂T饲料时,牡蛎幼虫似乎有能力重新合成固醇。甾醇合成依赖于膳食中甾醇的供给;在幼体发育阶段,饲喂T的幼虫比饲喂TCg的幼虫含有更多的甾醇。不同膳食制度下的幼虫甾醇组成表明可能的生物转化途径改变了膳食甾醇。喂食T的幼虫主要通过22-脱氢胆固醇中间体将饲料中的油菜甾醇转化为胆固醇。油菜甾醇在饲喂T和TCg的幼虫中也有活跃的合成,表明该甾醇可能在巨虾c.g . gigas幼虫中具有代谢作用。在所有实验条件下,去氨甾醇的明显合成表明它是一种膜成分或胆固醇合成的中间体。我们的数据还表明,巨螺幼虫需要大约13 ng胆固醇幼虫-1才能达到蜕变能力。这种质量平衡方法将允许确定幼虫营养的其他生化需求。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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