Hosono K, Kakuda H, Ichihara S
Laboratory of Microbiology, School of Agriculture, Nagoya University, Japan.
Biosci Biotechnol Biochem. 1995 Feb;59(2):256-61. doi: 10.1271/bbb.59.256.
Escherichia coli excretes acetate during aerobic growth in a rich medium, L-broth containing 0.4% glucose, and growth ceases before depletion of glucose because of the decrease in pH caused by the accumulation of acetate. The addition of sodium phosphate buffer to the medium allows cells to reuse the acetate accumulated. Reuse of the acetate, however, does not occur in the presence of remaining glucose. A gene on a multicopy plasmid was found to significantly decrease the accumulation of acetate by the transformant and the growth did not cease until depletion of both the glucose and acetate in the medium. The gene was tentatively named mlc (making large colonies). The putative Mlc protein has high hology with the NagC protein, which is a regulator protein in the nag operon responsible for the use of N-acetylglucosamine. The nagC gene on a multicopy plasmid also decreased the accumulation of acetate. Although the function of the genes in the phenomenon described is still unclear, transformants harboring the mlc gene or nagC gene on a multicopy plasmid will be useful for condensed cultivations involving glucose.
大肠杆菌在富含0.4%葡萄糖的丰富培养基L肉汤中需氧生长时会分泌乙酸盐，由于乙酸盐积累导致pH值下降，在葡萄糖耗尽之前生长就会停止。向培养基中添加磷酸钠缓冲液可使细胞重新利用积累的乙酸盐。然而，在有剩余葡萄糖存在的情况下，乙酸盐不会被重新利用。发现多拷贝质粒上的一个基因可显著减少转化体中乙酸盐的积累，并且直到培养基中的葡萄糖和乙酸盐都耗尽时生长才会停止。该基因被暂时命名为mlc（形成大菌落）。推测的Mlc蛋白与NagC蛋白具有高度同源性，NagC蛋白是nag操纵子中负责利用N - 乙酰葡糖胺的调节蛋白。多拷贝质粒上的nagC基因也减少了乙酸盐的积累。尽管所描述现象中这些基因的功能仍不清楚，但携带多拷贝质粒上mlc基因或nagC基因的转化体将有助于涉及葡萄糖的高密度培养。
