Russell J B
Agricultural Research Service, USDA and Section of Microbiology, Cornell University, Ithaca, NY 14853, USA.
J Anim Sci. 1998 Jul;76(7):1955-63. doi: 10.2527/1998.7671955x.
When ruminal bacteria have insufficient nitrogen and other nutrients, excess carbohydrate can be toxic. Pure cultures that are nitrogen-limited can convert only some of the excess carbohydrate to intracellular polysaccharide, but this pool can be quickly saturated. Fibrobacter succinogenes cultures that have excess cellobiose secrete glucose and cellotriose into the culture medium, and Prevotella ruminicola produces methylglyoxal, a highly toxic substance that causes a dramatic decrease in viability. Some ruminal bacteria (e.g., Streptococcus bovis and Selenomonas ruminantium) have mechanisms to decrease ATP production or spill the ATP that has already been produced. These mechanisms of decreasing intracellular ATP seem to protect the cell. Most ruminal bacteria can use ammonia as a nitrogen source, but amino nitrogen increases the growth efficiency of mixed ruminal bacteria. Amino nitrogen-dependent improvements in growth efficiency can be explained by an increase in growth rate and a decrease in energy spilling. Amino nitrogen is only beneficial if the rate of carbohydrate fermentation is rapid and carbohydrate is in excess.
当瘤胃细菌缺乏氮和其他营养物质时，过量的碳水化合物可能具有毒性。氮受限的纯培养物只能将部分过量的碳水化合物转化为细胞内多糖，但这个库很快就会饱和。含有过量纤维二糖的琥珀酸纤维杆菌培养物会将葡萄糖和纤维三糖分泌到培养基中，而瘤胃普雷沃氏菌会产生甲基乙二醛，这是一种剧毒物质，会导致存活率急剧下降。一些瘤胃细菌（如牛链球菌和反刍月形单胞菌）具有降低ATP生成或泄漏已生成的ATP的机制。这些降低细胞内ATP的机制似乎能保护细胞。大多数瘤胃细菌可以利用氨作为氮源，但氨基氮可提高混合瘤胃细菌的生长效率。生长效率的提高依赖氨基氮，这可以通过生长速率的增加和能量泄漏的减少来解释。只有在碳水化合物发酵速度快且碳水化合物过量时，氨基氮才有益。
