DNA replication in Escherichia coli 15T- growing at 20 degrees C

Effects of temperature on the size and shape of Escherichia coli cells

Two substrains of Escherichia coli B/r were grown to steady-state in batch cultures at temperatures between 22 and 42 degrees C in different growth media. The size and shape of the cells were measured from light and electron micrographs and with the Coulter channelizer. The results indicate that cells are shorter and somewhat thicker at the lower temperatures, especially in rich growth media; cell volume is then slightly smaller. A lower temperature was further found to increase the relative duration of the constriction period. The shapes of the cell size distributions are indistinguishable, indicating that the pattern of growth of the cells is the same at all temperatures. The adaptation of the cells to a temperature shift lasted several generations, indicating that the morphological effects of temperature are mediated by the cell's physiology.

Dimensions of Escherichia coli at various growth rates: model for envelope growth

The duplication of Escherichia coli B/r is described based on two independent sequences, the replication of the genome and the growth of the envelope. It is proposed that (i) new envelope growth zones are activated coincident with the initiation of new rounds of chromosome replication; (ii) each zone is active in envelope synthesis from the time of its inauguration to the division which follows the completion of the round of chromosome replication (that is, for C + D min); and (iii) the rate of envelope synthesis at each site is constant, independent of the growth rate. Measurements of the surface areas of two E. coli B/r substrains growing at a variety of rates and during nutritional transitions are consistent with the predictions of the model.

Growth response of Escherichia coli to nutritional shift-up: immediate division stimulation in slow-growing cells

When Escherichia coli 15T- cells growing exponentially at 70- to 80-min doubling times are subjected to a nutritional shift-up via glucose addition, cell division continues at the preshift rate for about 70 min (rate maintenance). The same cells growing at doubling times of 120 min or longer, however, begin to divide at a new faster rate immediately upon glucose addition. In both the rate maintenance and immediate division situations, cell mass, as measured by optical density (OD), begins to increase immediately upon shift-up. Consequently, the OD/cell pattern differs in the two growth-rate transitions. During rate maintenance, the OD/cell ratio increases dramatically for 60 to 70 min, and then slows appreciably and approaches the OD/cell characteristic of the new medium. During immediate division situations, the OD/cell increases only slightly for the first 180 +/- min; then the rate of increase accelerates but does not stop at the OD/cell characteristic of the new medium. Immediate division upon nutritional shift-up apparently depends upon initial doubling times in excess of 115 to 120 min and provision of a readily metabolized carbon source supporting doubling times of about 40 min. Similar immediate division occurs in E. coli B/r and K-12.

Direction of deoxyribonucleic acid replication in Escherichia coli under various conditions of cell growth

The direction of chromosome replication in a temperature-sensitive initiation mutant of Escherichia coli (CT28) is shown autoradiographically to be bidirectional. This mode of replication persists even when the rate of replication is reduced by slow growth in succinate minimal medium or in the presence of chloramphenicol. Therefore, although the rate of replication can be affected by certain physiological stimuli, the topology of replication need not be.

Initiation and termination of bacterial deoxyribonucleic acid replication in low concentrations of chloramphenicol

Escherichia coli 15T(-) can initiate a cycle of deoxyribonucleic acid replication with equal efficiency in the presence of 25 or 50 mug of chloramphenicol/ml. However, these replication cycles are not completed in the presence of these drug concentrations, and the amount of replication decreases with increasing drug concentration.

Chromosome replication and cell division in Escherichia coli at various temperatures of growth

The effect of temperature on the growth rate and the pattern of chromosome replication during the division cycle of Escherichia coli B/r growing in various media was investigated. The time between divisions, the time for a round of replication (C), and the time between completion of a round and cell division (D) were threefold longer at 21 C than at 37 C. At all temperatures and in all media, D equalled one-half C, suggesting that a common mechanism controls chromosome replication and the progression of the cell toward division after completion of a round of replication.