Initiation of deoxyribonucleic acid replication in Escherichia coli B: uncoupling from mass/deoxyribonucleic acid ratio

Rate maintenance of cell division in Escherichia coli B/r: analysis of a simple nutritional shift-down

A competitive (nonmetabolizable) inhibitor of glucose uptake, alpha-methylglucoside, was used to limit the growth of Escherichia coli. Cell division during such a nutritional shift-down was studied in batch cultures and with the "baby-machine" technique. Following a brief delay, the rate of division was maintained for 60 to 70 min in batch cultures and for an extended period in the baby machine. Decreases in cell size were due, in part, to a possible reduction in the mass per chromosome origin at the time of replication initiation and a shorter time interval between initiation and the subsequent division. These unusual findings suggest that this method for abrupt change in growth rate without modifying repression patterns is useful for studying the control of various aspects of the bacterial cell.

Unbalanced growth as a normal feature of development of Bdellovibrio bacteriovorus

In this study we have investigated the rates and spatial patterns of chromosome replication and cell elongation during the growth phase of wild-type facultatively prey-independent mutant strains of Bdellovibrio bacteriovorus. For the facultatively prey-independent mutants, the total DNA content of synchronously growing cultures was found to increase exponentially, as the multiple chromosomes within each filamentous cell replicated simultaneously. Cell mass, measured as total cellular protein, also increased exponentially during this period, apparently by means of multiple elongation sites along the filament wall. The relative rates of DNA and protein synthesis were unbalanced during growth, however, with the cellular concentration of DNA increasing slightly faster than that of protein. The original cellular DNA: protein ratio was restored in the progeny cells by continued protein synthesis during the septation period that follows the termination of DNA replication. Because of technical problems, these experiments could not be conducted on the wild-type cells, but similar results are assumed. This unusual pattern of unbalanced growth may represent an adaptation by bdellovibrios to maximize their progeny yield from the determinate amount of substrate available within a given prey cell.

Termination of DNA replication is required for cell division in Escherichia coli

The correlation between termination of DNA replication and cell division in Escherichia coli was studied under conditions in which DNA replication was slowed down without inducing SOS functions. The experimental system used involved amino acid starvation of synchronized cells in the presence of methionine. The results further support the essential correlation between termination of DNA replication and initiation of division processes.

Apparent minimal size required for cell division in Escherichia coli

The experiments described in this report were designed to find out whether there is a minimal size threshold for cell division or for DNA replication in Escherichia coli. Cells with decreasing size (or mass) were obtained by successive amino acid starvations. Following two starvations, the cells were at least 30% smaller than unstarved newborn cells. The results suggest that this size is below a minimal size threshold for cell division but not for initiation of DNA replication.

[The Escherichia coli cell cycle]

This review summarizes present knowledge of the bacterial cell cycle with particular emphasis on Escherichia coli. We discuss data coming from three different types of approaches to the study of cell extension and division: The search for discrete events occurring once per division cycle. It is generally agreed that the initiation and termination of DNA replication and cell septation are discrete events; there is less agreement on the sudden doubling in rate of cell surface extension, murein biosynthesis and the synthesis of membrane proteins and phospholipids. We discuss what is known about the temporal relationship amongst the various cyclic events studied. The search for discrete growth zones in the cell envelope layers. We discuss conflicting reports on the existence of murein growth zones and protein insertion sites in the inner and outer membranes. Elucidation of the mechanism regulating the initiation of DNA replication. The concept of "critical initiation mass" is examined. We review data suggesting that the DNA is attached to the envelope and discuss the role of the latter in the initiation of DNA replication.

Changes in cell dimensions during amino acid starvation of Escherichia coli

Electron microscopic analysis was used to study cells of Escherichia coli B and K-12 during and after amino acid starvation. The results confirmed our previous conclusion that cell division and initiation of DNA replication occur at a smaller cell volume after amino acid starvation. Although during short starvation periods, the number of constricting cells decreased due to residual division, it appears that during prolonged starvation, cells of E. coli B and K-12 were capable of initiating new constrictions. During amino acid starvation, cell diameter decreased significantly. The decrease was reversed only after two generation times after the resumption of protein synthesis and was larger in magnitude than that previously observed before division (F. J. Trueba and C. L. Woldringh, J. Bacteriol. 142:869-878, 1980). This decrease in cell diameter correlates with synchronization of cell division which has been shown to occur after amino acid starvation.

Bacterial growth and division: genes, structures, forces, and clocks

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