猪肠道色氨酸利用菌调节小肠代谢色氨酸的规律及机制研究

Dietary amino acids (AA) are important for the growth and health of animals. However, the utilization efficiency of dietary AA is low which makes big loss for the pig industry. The small intestine is the most important site for the absorption and metabolism of dietary AA. During the small intestinal absorption, tryptophan as one of the most important indispensable AA for pigs is metabolized in the small-intestinal mucosal cell and produces many important metabolites such as serotonin, which regulates nutrients absorption and metabolism in the body. Meanwhile, recent finding revealed that the pig small intestine harbors several species of amino acid-metabolizing bacteria including the tryptophan-metabolizing bacteria which community composition can be altered by the process of small-intestinal transport and metabolism of tryptophan. Therefore, it is of utmost important to unravel the detail mode of action and underlying mechanism during the host-microbe co-metabolism of tryptophan and the impact on the tryptophan utilization and luminal ecology in the small intestine. This study plans to use pig as animal model and investigates the metabolism of tryptophan in the small intestine. We will investigate the effects of the small-intestinal tryptophan-metabolizing bacteria on the small-intestinal utilization and metabolism of tryptophan and related mode of action. To answer the above questions will help to improve the utilization efficiency and functionality of dietary amino acids and provide novel ideas for the development of new strategies in promoting the growth and health of pigs.

日粮氨基酸利用率不高一直是猪生产中存在的问题，这不仅造成饲料的浪费更对环境产生负面影响。小肠是吸收日粮氨基酸的主要部位，在转运吸收日粮氨基酸的同时对氨基酸有代谢作用。在吸收过程中，日粮色氨酸有相当部分被小肠利用，经小肠代谢产生的5-羟色胺等代谢物，影响机体对养分的吸收与代谢。同时，肠道中存在大量的氨基酸代谢细菌（包括色氨酸利用菌），其组成及氨基酸利用代谢模式可能与肠道对氨基酸（特别是色氨酸）的转运及代谢偶联。因此，有必要研究其中的具体作用模式及可能机制。本研究以猪为研究对象，以肠道色氨酸的利用及代谢为切入点，研究小肠色氨酸利用菌对小肠利用代谢色氨酸及产生重要代谢物（如5-羟色胺等）的影响及可能作用机制。从而为提高日粮氨基酸的利用效率及功能的发挥，促进猪的生长和健康，实现可持续猪生产，提供新思路，开辟新途径。

肠道微生物影响小肠对日粮蛋白质与氨基酸的消化吸收，这不仅影响猪生产的效率还影响生产的可持续性。因此，研究肠道中氨基酸利用与代谢相关微生物显得十分重要。本项目以猪小肠中的色氨酸（日粮必需氨基酸）利用与代谢为切入点，对猪小肠中色氨酸利用菌进行了分离，并对其色氨酸利用代谢特性进行了研究。首先建立了同时检测分析细菌培养液中游离氨基酸（包括色氨酸）及八种色氨酸代谢物的液相色谱方法。通过肠道微生物体外厌氧稀释与继代培养方法，从猪回肠内容物中分离筛选获得了三株色氨酸利用菌，经分子鉴定三株细菌均为克雷伯氏菌（Klebsiella）属细菌。三株细菌可在体外培养条件下，利用色氨酸并产生吲哚乙酸。通过分析计算可知，三株色氨酸利用菌只代谢少量利用的色氨酸产生吲哚乙酸，大部分利用的色氨酸可能用于细菌的蛋白质合成及生成其它代谢产物。利用稀释-PCR研究了克雷伯氏菌属细菌在猪回肠中的丰度，结果显示该菌是猪回肠中的优势细菌。本研究分离获得的色氨酸利用菌可为后续体内外实验提供材料，研究色氨酸利用菌及其代谢物对小肠细胞生理及代谢的影响。研究结果可为探明小肠中氨基酸的代谢与吸收机制及日粮措施改善肠道对氨基酸利用率，促进动物生长与健康，提供研究基础。