Nitrogen is a most important nutrient resource for Escherichia coli and other bacteria that harbor the glnKamtB operon, a high-affinity ammonium uptake system highly interconnected with cellular metabolism. Although this system confers an advantage to bacteria when growing under nitrogen-limiting conditions, little is known about the impact of these genes on microbial fitness under nutrient-rich conditions. Here, the genetically tractable E. coli BW25113 strain and its glnKamtB-null mutant (JW0441) were used to analyze the impact of GlnK-AmtB on growth rates and oxidative stress tolerance. Strain JW0441 showed a shorter initial lag phase, higher growth rate, higher citrate synthase activity, higher oxidative stress tolerance and lower expression of serA than strain BW25113 under nutrient-rich conditions, suggesting a fitness cost to increase metabolic plasticity associated with serine metabolism. The overexpression of serA in strain JW0441 resulted in a decreased growth rate and stress tolerance in nutrient-rich conditions similar to that of strain BW25113, suggesting that the negative influence on bacterial fitness imposed by GlnK-AmtB can be traced to the control of serine biosynthesis. Finally, we discuss the potential applications of glnKamtB mutants in bioproduction processes.

中文翻译：

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消除 GlnKAmtB 影响丝氨酸生物合成并改善大肠杆菌在营养丰富的条件下的生长和胁迫耐受性

氮是大肠杆菌和其他携带glnKamtB操纵子的细菌最重要的营养资源，glnKamtB操纵子是一种与细胞代谢高度相关的高亲和力铵吸收系统。尽管该系统在氮限制条件下生长时为细菌带来了优势，但人们对这些基因在营养丰富的条件下对微生物适应性的影响知之甚少。在这里，遗传易处理的大肠杆菌BW25113 菌株及其glnKamtB-null 突变体 (JW0441) 用于分析 GlnK-AmtB 对生长速率和氧化应激耐受性的影响。在营养丰富的条件下，菌株 JW0441 显示出比菌株 BW25113 更短的初始滞后期、更高的生长速率、更高的柠檬酸合酶活性、更高的氧化应激耐受性和更低的serA表达，这表明增加与丝氨酸代谢相关的代谢可塑性的健身成本。菌株 JW0441中serA的过表达导致与菌株 BW25113 相似的营养丰富条件下的生长速率和胁迫耐受性降低，这表明 GlnK-AmtB 对细菌适应性的负面影响可以追溯到丝氨酸生物合成的控制. 最后，我们讨论了潜在的应用生物生产过程中的glnKamtB突变体。