Hailemariam Samson, Zhao Shengguo, He Yue, Wang Jiaqi
State Key Laboratory of Animal Nutrition, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
Dilla University, College of Agriculture and Natural Resource, Dilla P. O. Box 419, Ethiopia.
Anim Nutr. 2021 Dec;7(4):989-996. doi: 10.1016/j.aninu.2021.07.002. Epub 2021 Sep 14.
Inefficient dietary nitrogen (N) conversion to microbial proteins, and the subsequent use by ruminants, is a major research focus across different fields. Excess bacterial ammonia (NH) produced due to degradation or hydrolyses of N containing compounds, such as urea, leads to an inefficiency in a host's ability to utilize nitrogen. Urea is a non-protein N containing compound used by ruminants as an ammonia source, obtained from feed and endogenous sources. It is hydrolyzed by ureases from rumen bacteria to produce NH which is used for microbial protein synthesis. However, lack of information exists regarding urea hydrolysis in ruminal bacteria, and how urea gets to hydrolysis sites. Therefore, this review describes research on sites of urea hydrolysis, urea transport routes towards these sites, the role and structure of urea transporters in rumen epithelium and bacteria, the composition of ruminal ureolytic bacteria, mechanisms behind urea hydrolysis by bacterial ureases, and factors influencing urea hydrolysis. This review explores the current knowledge on the structure and physiological role of urea transport and ureolytic bacteria, for the regulation of urea hydrolysis and recycling in ruminants. Lastly, underlying mechanisms of urea transportation in rumen bacteria and their physiological importance are currently unknown, and therefore future research should be directed to this subject.
日粮氮（N）向微生物蛋白的低效转化以及反刍动物随后对其的利用，是不同领域的主要研究重点。含氮化合物（如尿素）降解或水解产生的过量细菌氨（NH），会导致宿主利用氮的能力低下。尿素是反刍动物用作氨源的一种非蛋白含氮化合物，可从饲料和内源性来源获得。它被瘤胃细菌的脲酶水解产生NH，用于微生物蛋白合成。然而，关于瘤胃细菌中尿素水解以及尿素如何到达水解位点的信息尚缺。因此，本综述描述了关于尿素水解位点、尿素向这些位点的转运途径、瘤胃上皮和细菌中尿素转运体的作用及结构、瘤胃尿素分解菌的组成、细菌脲酶水解尿素的机制以及影响尿素水解的因素等方面的研究。本综述探讨了目前关于尿素转运和尿素分解菌的结构及生理作用的知识，以调控反刍动物的尿素水解和再循环。最后，瘤胃细菌中尿素转运的潜在机制及其生理重要性目前尚不清楚，因此未来的研究应针对这一主题。
