猪后肠真菌对不同类型日粮纤维的响应模式及利用机理解析

作为猪肠道的一类常驻微生物，真菌占比不足0.1%，其组成和营养学意义知之甚少。申请人前期发现，猪后肠真菌群落结构特殊；日粮纤维（DF）来源和碳水化合物组合模式与真菌多样性有关；一些可产生碳水化合物活性酶（CAZymes）的真菌与菊粉和微晶纤维素（MCC）含量高度相关。由于CAZymes具有菌种和底物特异性，推测其表达调控可能是真菌对DF进行选择性利用的关键。故本项目将分别以菊粉和MCC为两种类型DF，首先通过在体试验比较分析猪后肠真菌网络对两种DF的响应规律，并分离特异性利用两种DF的真菌菌株；再通过差异菌株的比较培养，揭示猪后肠真菌CAZymes针对两种DF的表达特征；最后以构成不同DF的糖组分为诱导碳源，探明DF酶解产物对真菌CAZymes表达的反馈调节途径，从整体、菌群、菌株三个层面系统解析猪后肠真菌对DF的选择性利用机理，为深入研究猪纤维营养和后肠营养提供参考。

As resident symbionts in swine gut, fungi account for less than 0.1% of total microorganisms. So far, the fungal composition and nutritional significance in the gut of pigs is poorly understood. According to the results of our previous studies, the community of fungi in the hindgut of pigs showed particularly distinct from that of human and mice. The sources of dietary fibers (DFs) and the composite patterns of dietray carbohydrates were also observed to be related to the fungal diversity. In addition, the content of inulin and microcrystalline cellulose (MCC) was investigated to be highly associated with the abundance of those fungi producing carbohydrate active enzymes (CAZymes). Due to the species- and substrate- specialty of CAZymes, it can be speculated that the regulation of CAZymes’ expression may be the keystone of fungi to selectively utilize different DFs. Therefore, in the upcoming studies, inulin and MCC will be continuously used as two types of DFs. An in vivo experiment will be firstly conducted to compare the response of fungal community in the hindgut of pigs to the two different DFs, and fungal strains involved in the utilization of the two DFs will be isolated. Next, the different isolates targeting the two DFs will be anaerobically cultured to compare and reveal the corresponding relationship between the expression of fungal CAZymes and DFs. Finally, the main monosaccharides or cellobiose constituting DFs will be used as sole carbon sources in the culture to illustrate their feedback regulation to the expression of fungal CAZymes. Together, the mechanism underlying the selective utilization of fungi to different DFs in the hindgut of pigs will be systematically expounded. Results will provide new thoughts for further studies on the nutritional function of DFs and microflora in the hindgut of pigs.