Changes in Viability, Cell Composition, and Enzyme Levels During Starvation of Continuously Cultured (Ammonia-Limited) Selenomonas ruminantium
Changes in Viability, Cell Composition, and Enzyme Levels During Starvation of Continuously Cultured (Ammonia-Limited) Selenomonas ruminantium
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连续培养（限氨）反刍硒单胞菌饥饿期间活力、细胞组成和酶水平的变化
DOI：
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发表时间：
1982
影响因子：
4.4
通讯作者：
R. Hespell
中科院分区：
文献类型：
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作者：
R. Mink;J. Patterson;R. Hespell
在氮（氨）限制的连续培养条件下，瘤胃厌氧菌反刍硒单胞菌以不同的稀释率生长（D）。存活种群的比例随着 D 的增加而增加，在 D = 0.5 h−1 时为 91%。洗涤后的细胞悬液在 39°C 下进行长期营养饥饿。所有种群的活力均呈现对数线性下降，且与生长率相关。在 D = 0.05、0.20 和 0.50 下生长的细胞分别在 8.1、4.6 和 3.6 小时后失去约 50% 的活力。无论稀释率如何，总细胞数的线性下降率显着降低且保持恒定。所有主要细胞成分在饥饿期间都会下降，其中 RNA 的下降速度最大，其次是 DNA、碳水化合物、细胞干重和蛋白质。随着细胞在较高 D 值下生长，RNA 损失率增加，而碳水化合物损失率则相反。大部分降解的 RNA 没有被分解代谢，而是排泄到悬浮缓冲液中。在所有 D 值下，反刍链球菌在生长过程中主要产生乳酸盐和少量的乙酸盐、丙酸盐和琥珀酸盐。饥饿时，仅产生少量的乙酸盐。与单独的缓冲液相比，向悬浮缓冲液中添加葡萄糖、维生素或两者或在用过的培养基中饥饿会导致更大的活力损失。对饥饿细胞提取物的检查表明，果糖二磷酸醛缩酶和乳酸脱氢酶活性保持相对恒定。饥饿期间脲酶和谷氨酸脱氢酶活性逐渐下降，而谷氨酰胺合成酶活性略有增加。数据表明，氮（氨）有限的反刍葡萄球菌细胞的生存能力有限，但这种能力大于先前发现的能量（葡萄糖）有限的细胞。显然没有一种细胞成分可以作为内源代谢的分解代谢底物。相对于活力的丧失，细胞酶是稳定的，这表明非活力细胞保持潜在的代谢活性，并且普遍的、非特异性的酶降解不是导致活力丧失的主要因素。
Under nitrogen (ammonia)-limited continuous culture conditions, the ruminal anaerobe Selenomonas ruminantium was grown at various dilution rates (D). The proportion of the population that was viable increased with D, being 91% at D = 0.5 h−1. Washed cell suspensions were subjected to long-term nutrient starvation at 39°C. All populations exhibited logarithmic linear declines in viability that were related to the growth rate. Cells grown at D = 0.05, 0.20, and 0.50 lost about 50% viability after 8.1, 4.6, and 3.6 h, respectively. The linear rates of decline in total cell numbers were dramatically less and constant regardless of dilution rate. All major cell constituents declined during starvation, with the rates of decline being greatest with RNA, followed by DNA, carbohydrate, cell dry weight, and protein. The rates of RNA loss increased with cells grown at higher D values, whereas the opposite was observed for rates of carbohydrate losses. The majority of the degraded RNA was not catabolized but was excreted into the suspending buffer. At all D values, S. ruminantium produced mainly lactate and lesser amounts of acetate, propionate, and succinate during growth. With starvation, only small amounts of acetate were produced. Addition of glucose, vitamins, or both to the suspending buffer or starvation in the spent culture medium resulted in greater losses of viability than in buffer alone. Examination of extracts made from starving cells indicated that fructose diphosphate aldolase and lactate dehydrogenase activities remained relatively constant. Both urease and glutamate dehydrogenase activities declined gradually during starvation, whereas glutamine synthetase activity increased slightly. The data indicate that nitrogen (ammonia)-limited S. ruminantium cells have limited survival capacity, but this capacity is greater than that found previously with energy (glucose)-limited cells. Apparently no one cellular constituent serves as a catabolic substrate for endogenous metabolism. Relative to losses in viability, cellular enzymes are stable, indicating that nonviable cells maintain potential metabolic activity and that generalized, nonspecific enzyme degradation is not a major factor contributing to viability loss.