Prüss B M, Matsumura P
Department of Microbiology and Immunology, University of Illinois at Chicago 60612-7344, USA.
J Bacteriol. 1996 Feb;178(3):668-74. doi: 10.1128/jb.178.3.668-674.1996.
The role of an activator of flagellar transcription in Escherichia coli, flhD, was investigated in the regulation of cell division. When grown in tryptone broth, flhD mutant cells divided exponentially until they reached a cell density of 2.5 x 10(9) cells per ml. Wild-type cells and flhC mutant cells divided exponentially until they reached a cell density of 4 x 10(7) cells per ml. flhD mutant cells divided 5 times more than wild-type cells before they reduced their cell division rate and reached a cell density 37 times higher than that of wild-type or flhC mutant cultures. In stationary phase, the biomasses of all cultures were similar; however, flhD mutant cells were significantly smaller. Additional tryptone, Casamino Acids, and individual amino acids, added at the beginning of growth, allowed wild-type cells to grow to higher cell densities. Serine was determined to have the greatest effect. In contrast, the addition of Casamino Acids did not exhibit an effect upon flhD mutant cells. flhD mutant cells exhibited normal rates of uptake of serine and other amino acids. In both wild-type and flhD mutant cultures, the concentrations of serine in the media dropped from 140 to 20 microM within the first 2 h of growth. Serine concentrations and cell division rates were highly correlated. Wild-type cells reduced their cell division rate at a medium concentration of 50 microM serine, and the addition of serine at this time caused cells to resume a higher rate of division. We conclude that the reduction of the cell division rate in wild-type cells is caused by the depletion of serine from the medium and that flhD mutant cells seem to be unable to sense this depletion.
研究了大肠杆菌中鞭毛转录激活因子flhD在细胞分裂调控中的作用。在胰蛋白胨肉汤中培养时，flhD突变细胞呈指数分裂，直至细胞密度达到每毫升2.5×10⁹个细胞。野生型细胞和flhC突变细胞呈指数分裂，直至细胞密度达到每毫升4×10⁷个细胞。flhD突变细胞在降低细胞分裂速率并达到比野生型或flhC突变培养物高37倍的细胞密度之前，分裂次数比野生型细胞多5倍。在稳定期，所有培养物的生物量相似；然而，flhD突变细胞明显较小。在生长开始时添加额外的胰蛋白胨、酪蛋白氨基酸和单个氨基酸，可使野生型细胞生长至更高的细胞密度。已确定丝氨酸的作用最大。相比之下，添加酪蛋白氨基酸对flhD突变细胞没有影响。flhD突变细胞对丝氨酸和其他氨基酸的摄取速率正常。在野生型和flhD突变培养物中，培养基中丝氨酸的浓度在生长的前2小时内从140微摩尔降至20微摩尔。丝氨酸浓度与细胞分裂速率高度相关。野生型细胞在丝氨酸浓度为50微摩尔时降低其细胞分裂速率，此时添加丝氨酸会使细胞恢复更高的分裂速率。我们得出结论，野生型细胞中细胞分裂速率的降低是由培养基中丝氨酸的耗尽引起的，并且flhD突变细胞似乎无法感知这种耗尽。
