瘤胃源酵母的分离筛选及对不同底物发酵能力影响

Isolation and characterization of rumen yeast and an evaluation of its effect on ruminal fermentation with different types of substrate

本实验旨在分离筛选瘤胃源酵母,研究其对不同饲料底物的发酵特性。实验以山羊及奶牛瘤胃液为菌源,利用酵母选择性培养基,通过分离筛选、生长曲线测定和26SrDNA鉴定,获得1株生长速度较快的Meyerozyma属酵母菌株。在此基础上,采用体外发酵技术,分别以羊草与精料混合物、马铃薯淀粉和玉米淀粉为底物,以奶牛瘤胃液为接种物,研究该酵母菌株对瘤胃微生物体外发酵参数的影响。结果表明,在以羊草和精料混合物为底物时,添加瘤胃源酵母显著降低了发酵液pH和乳酸浓度(P<0.001),显著提高了丙酸浓度和干物质消失率(P<0.05);以玉米淀粉为底物时,添加该酵母菌显著降低了发酵液pH和乳酸浓度(P<0.001);以马铃薯淀粉为底物时,显著降低了pH(P<0.05),提高了丙酸浓度(P<0.05);但在上述3种底物条件下,添加酵母菌对发酵液中总产气量、氨态氮、乙酸、丁酸、异丁酸、戊酸和异戊酸浓度无显著影响(P>0.05)。采用Real-time PCR测定结果表明,添加该酵母菌可显著提高以羊草和马铃薯淀粉为底物时发酵液中总菌16SrDNA的挎贝数(P<0.05)。结果说明,本研究分离获取的瘤胃源酵母可提高瘤胃微生物对羊草精料混合物的降解能力,降低羊草精料混合物组和玉米淀粉组发酵液中乳酸浓度,提示该菌株可能具有提高日粮消化利用效率、促进丙酸生成和瘤胃细菌生长的作用。

This study was conducted to isolate rumen yeast and evaluate its possible role in changing fermenta tion characteristics by using in vitro fermentation with three different substrates. A yeast strain with a fast growth rate belonging to the Meyerozyma genus was isolated through screening, growth curve determination and identification of 26S rDNA using a selective medium of yeast composed of goat and dairy cow ruminal fluid. The effect of this isolated culture on ruminal fermentation was evaluated with three substrates： Chinese wildrye plus concentrate mixture, potato starch and corn starch. Ruminal fluid from dairy cattle was used as an inocu lant. The results showed that with the Chinese wildrye plus concentrate mixture as substrate, yeast addition decreased ruminal pH and the concentration of lactic acid （P〈0. 001）, while it increased the concentration of propionic acid and the digestibility of dry matter （P〈0.05）. The addition of yeast decreased ruminal pH and lactic concentration （P〈0. 001） in the corn starch substrate. Moreover, the addition of yeast culture decreased ruminal pH （P〈0.05） and increased the concentration of propionic acid （P〈0.05）. However, total gas pro duction and concentrations of ammonia-N, acetic acid, butyric acid, isobutyric acid, valeric acid and isovaleric acid were not affected （P〉0.05） by yeast addition in the three substrate groups. The real-time PCR data showed that isolate addition increased the number of total bacteria in the Chinese wildrye plus concentrate and potato starch substrates. Results indicate that the rumen yeast isolates can improve the rumen＇s dietary degra dation capability and reduce lactic acid levels for the Chinese wildrye plus concentrate and corn starch sub strates. This suggests that the yeast isolates could improve digestibility efficiency in ways that enhance the pro pionate production and the growth of ruminal bacteria.