Broach J, Neumann C, Kustu S
J Bacteriol. 1976 Oct;128(1):86-98. doi: 10.1128/jb.128.1.86-98.1976.
We have isolated mutant strains (nit) of Salmonella typhimurium that are defective in nitrogen metabolism. They have a reduced ability to use a variety of compounds including glutamate, proline, arginine, N-acetyl-glucosamine, alanine, and adenosine as sole nitrogen source. In addition, although they grow normally on high concentrations of ammonium chloride (greater than 1 mM) as nitrogen source, they grow substantially more slowly than wild type at low concentrations (less than 1 mM). We postulated that the inability of these strains to utilize low concentrations of ammonium chloride accounts for their poor growth on other nitrogen sources. The specific biochemical lesion in strains with a nit mutation is not known; however, mutant strains have no detectable alteration in the activities of glutamine synthetase, glutamate synthetase, or glutamate dehydrogenase, the enzymes known to be involved in assimilation of ammonia. A nit mutation is suppressed by second-site mutations in the structural gene for glutamine synthetase (glnA) that decrease glutamine synthetase activity.
我们已经分离出鼠伤寒沙门氏菌的突变菌株（nit），这些菌株在氮代谢方面存在缺陷。它们利用包括谷氨酸、脯氨酸、精氨酸、N-乙酰葡糖胺、丙氨酸和腺苷在内的多种化合物作为唯一氮源的能力降低。此外，尽管它们在高浓度氯化铵（大于1 mM）作为氮源时能正常生长，但在低浓度（小于1 mM）时生长速度比野生型慢得多。我们推测，这些菌株无法利用低浓度氯化铵是它们在其他氮源上生长不良的原因。具有nit突变的菌株中具体的生化损伤尚不清楚；然而，突变菌株在谷氨酰胺合成酶、谷氨酸合成酶或谷氨酸脱氢酶（已知参与氨同化的酶）的活性方面没有可检测到的变化。谷氨酰胺合成酶（glnA）结构基因中的第二位点突变可抑制nit突变，该突变会降低谷氨酰胺合成酶的活性。
