Atasoglu C, Valdés C, Walker N D, Newbold C J, Wallace R J
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, United Kingdom.
Appl Environ Microbiol. 1998 Aug;64(8):2836-43. doi: 10.1128/AEM.64.8.2836-2843.1998.
The influence of peptides and amino acids on ammonia assimilation and de novo synthesis of amino acids by three predominant noncellulolytic species of ruminal bacteria, Prevotella bryantii B14, Selenomonas ruminantium HD4, and Streptococcus bovis ES1, was determined by growing these bacteria in media containing 15NH4Cl and various additions of pancreatic hydrolysates of casein (peptides) or amino acids. The proportion of cell N and amino acids formed de novo decreased as the concentration of peptides increased. At high concentrations of peptides (10 and 30 g/liter), the incorporation of ammonia accounted for less than 0.16 of bacterial amino acid N and less than 0.30 of total N. At 1 g/liter, which is more similar to peptide concentrations found in the rumen, 0.68, 0.87, and 0.46 of bacterial amino acid N and 0.83, 0.89, and 0.64 of total N were derived from ammonia by P. bryantii, S. ruminantium, and S. bovis, respectively. Concentration-dependent responses were also obtained with amino acids. No individual amino acid was exhausted in any incubation medium. For cultures of P. bryantii, peptides were incorporated and stimulated growth more effectively than amino acids, while cultures of the other species showed no preference for peptides or amino acids. Apparent growth yields increased by between 8 and 57%, depending on the species, when 1 g of peptides or amino acids per liter was added to the medium. Proline synthesis was greatly decreased when peptides or amino acids were added to the medium, while glutamate and aspartate were enriched to a greater extent than other amino acids under all conditions. Thus, the proportion of bacterial protein formed de novo in noncellulolytic ruminal bacteria varies according to species and the form and identity of the amino acid and in a concentration-dependent manner.
通过在含有15NH4Cl以及添加了不同量酪蛋白胰蛋白酶水解物（肽）或氨基酸的培养基中培养三种主要的非纤维素分解瘤胃细菌——布氏普雷沃氏菌B14、反刍月形单胞菌HD4和牛链球菌ES1，测定了肽和氨基酸对氨同化以及氨基酸从头合成的影响。随着肽浓度的增加，细胞氮和从头合成的氨基酸的比例降低。在高浓度肽（10和30 g/升）时，氨的掺入占细菌氨基酸氮的比例不到0.16，占总氮的比例不到0.30。在1 g/升时（更接近瘤胃中发现的肽浓度），布氏普雷沃氏菌、反刍月形单胞菌和牛链球菌的细菌氨基酸氮分别有0.68、0.87和0.46以及总氮分别有0.83、0.89和0.64来自氨。氨基酸也呈现出浓度依赖性反应。在任何孵育培养基中都没有单个氨基酸被耗尽。对于布氏普雷沃氏菌培养物，肽的掺入和对生长的刺激比氨基酸更有效，而其他菌种的培养物对肽或氨基酸没有偏好。当每升培养基中添加1 g肽或氨基酸时，视菌种不同，表观生长产量提高了8%至57%。当向培养基中添加肽或氨基酸时，脯氨酸的合成大大减少，而在所有条件下，谷氨酸和天冬氨酸比其他氨基酸富集程度更高。因此，非纤维素分解瘤胃细菌中从头合成的细菌蛋白质的比例因菌种、氨基酸的形式和种类以及浓度依赖性方式而异。
