Takagi T, Sugiura M, Kisumi M
J Biochem. 1986 Feb;99(2):357-64. doi: 10.1093/oxfordjournals.jbchem.a135490.
Arginine productivity of an arginine-producing mutant of Serratia marcescens decreased during successive batch culturing. The mutant grew more slowly than the parent strains in a minimal medium, and spontaneously produced derivatives that grew more rapidly than the mutant. A large majority of the derivatives required N-acetylglutamate or arginine for growth, due to lack of N-acetylglutamate synthase, the argA gene product. The argA1 allele carried by the mutant was found to be relatively unstable. While the mutation rate in a stable argA mutant allele was less than 1 X 10(-8) per cell per generation, that in the argA1 allele was 9 X 10(-7). The instability of the arginine productivity, therefore, was owing to both a disadvantage of the mutant in growth and a high mutability in the argA1 allele. In addition to the auxotrophs, the unstable arginine-producing mutant spontaneously produced at low frequency stable arginine-producing derivatives; among them, AT428 formed N-acetylglutamate synthase with a reduced affinity for glutamic acid. The derivative showed restored capability for propagation, and stably produced a large amount of arginine in the presence of glutamic acid or fumaric acid. By transductional analysis, the derivative was found to have acquired in the argA allele an additional mutation leading to the reduced affinity independently of the original one leading to the feedback-resistant enzyme.
粘质沙雷氏菌精氨酸生产突变株在连续分批培养过程中精氨酸产量下降。该突变株在基本培养基中生长比亲本菌株慢，并自发产生比突变株生长更快的衍生物。由于缺乏N - 乙酰谷氨酸合酶（argA基因产物），大多数衍生物生长需要N - 乙酰谷氨酸或精氨酸。发现该突变株携带的argA1等位基因相对不稳定。稳定的argA突变等位基因的突变率低于每细胞每代1×10^(-8)，而argA1等位基因的突变率为9×10^(-7)。因此，精氨酸产量的不稳定性是由于突变株生长方面的劣势以及argA1等位基因的高突变性。除了营养缺陷型，不稳定的精氨酸生产突变株还以低频率自发产生稳定的精氨酸生产衍生物；其中，AT428形成了对谷氨酸亲和力降低的N - 乙酰谷氨酸合酶。该衍生物显示出恢复的繁殖能力，并且在谷氨酸或富马酸存在下稳定地产生大量精氨酸。通过转导分析，发现该衍生物在argA等位基因中获得了一个额外的突变，导致亲和力降低，这与导致反馈抗性酶的原始突变无关。
