Changes in Cell Size and Shape Associated with Changes in the Replication Time of the Chromosome ofEscherichia coli

Abstract

Average cell mass is shown to be inversely related to the concentration of thymine in the growth medium of a thystrain of Escherichia coli. The kinetics of the transition from one steady-state average cell mass to another was followed in an attempt to determine the relationship between the chromosome replication time and the time between completion of a round of chromosome replication and the subsequent cell division. Differences in average cell mass are shown to be associated with similar differences in average cell volume. Changes in volume associated with changes in thymine concentration are shown to be due primarily to differences in the width of cells. It is proposed that extension in length of the cell envelope occurs at a linear rate which is proportional to the growth rate and which doubles at the time of termination of rounds of replication. Changes in volume not associated with a change in growth rate are therefore accommodated by a change in cell width. Conditions are described under which average cell mass can continue to increase in successive generations and no steady-state average cell mass is achieved.

Replication fork and SeqA focus distributions in Escherichia coli suggest a replication hyperstructure dependent on nucleotide metabolism

“…These results are in agreement with the observation that thymine-limited cells of strain CR34 are larger than the wild type (Zaritsky et al, 1999). This increment of mass is accommodated by extension in both length and diameter (Zaritsky and Pritchard, 1973;Woldringh et al, 1994).…”

Abnormal Metabolism of Thymidine Nucleotides and Phosphorylation of Deoxycytidine in Escherichia coli C thy- ura- Mutant

“…This reduction of the dCTP pool causes a decreased rate of DNA replication. As a result, this reduced DNA replication reduces the DNA concentration (Table 1) as reported by Pritchard [4] and Pritchard and Zaritsky [3]. Although the rate of DNA synthesis in the dCyd-added culture increases twofold compared to that in its culture without addition (Fig.5), the dTTP pool in the dCyd-added culture does not decrease to one-half but increases to twice that of its culture without added dCyd.…”

“…in the growth rate of a thy+ culture has exactly the same effect on DNA concentration [3,4]. One mutant (Thy A-35) isolated here from E. coli C strain by aminopterin treatment shows a rate of DNA replication lower than that of other mutants under the same conditions.…”

Localizing cell division in sphericalEscherichia coliby nucleoid occlusion

“…To visualize consecutive constrictions in a single cell early enough, the time D between replication termination and cell separation must be extended or division conditions enhanced, at least temporarily. This is obtained by manipulating the chromosome replication time C in thyA strains using thymine 'steps' [21]. Slower replication/segregation delays termination and hence the subsequent division.…”

“…That is why thymine auxotrophs growing with a low thymine concentration form larger cells with more complex nucleoids and more DNA without any change in mass growth rate [17]. The larger cell size is accommodated by a gradual increase in diameter [21] resulting in extended time to ¢nalize division. Stepping up the concentration of thymine (thus replication rate) increases temporarily the frequency of terminations.…”