Division pattern of a round mutant of Escherichia coli

Abstract

A round mutant of Escherichia coli, when grown in Methocel medium, forms chains of cells and does not form tetrads. This implies that successive division planes of the round mutant are parallel rather than perpendicular. These results differ from a previous proposal that division planes in this round mutant are perpendicular to the prior division plane (W. D. Donachie, S. Addinall, and K. Begg, Bioessays 17:569-576, 1995).When round mutants were originally isolated, they were conditional (temperature-sensitive) cells (10). Recently, Donachie et al. (9) have produced a nonconditional, stable, round mutant of Escherichia coli. They reported that divisions occur with successive planes of division positioned at right angles to each other. This conclusion is derived from the observation that cells growing on agar produced four-cornered tetrads, or square arrangements, at the four-cell stage. Tetrad formation is explained by the alternation of successive division planes, with a division plane occurring perpendicular to the previous division plane. This pattern differs from the parental, rod-shaped cell, where successive division planes are parallel.If the tetrad-forming ability of round cells (due to alternation of planes of division) is real, then there are problems reconciling this growth pattern with the hoop-between-hoop model for normal cell growth. Rod-shaped E. coli cells are believed to grow in the side wall by the insertion of new hoops of peptidoglycan between old hoops (1-4). Hoops run circumferentially around the cell, perpendicular to the long axis. If this peptidoglycan insertion mechanism is retained in the round mutant, then it is difficult to imagine how planes of division can occur perpendicular to the previous division plane. The alternate division plane pattern would entail cutting through, rather than insertion between, preexisting hoops.

Tertiary Structure of Bacterial Murein: the Scaffold Model

“…However, the concept runs directly into conflict with the fact that spheroid E. coli cells, like those of some gram-negative cocci (58) and many gram-positive spheroid bacteria, e.g., S. aureus (19,54,61), are able to alternate the division plane. Indeed, this biological fact implies that after each division, the cell either has to change the entire pattern of murein assembly (9) or produce progeny with two or three different types of murein architecture within one cell. The "segregated sectors" on the murein surface of dividing spheroid E. coli cells were recently discovered (11), and the question of whether such sectors of one cell really do possess a different architecture arises.…”

“…Generally, strands could run either parallel with or perpendicular to the plasma membrane to build up a planar network (regular or irregular) or a vertically oriented matrix, respectively. According to the predominant concept, glycan chains are arranged in parallel with the plasma membrane, are aligned in a head-to-tail manner, and are oriented perpendicularly to the cell axis (8,9,29). Taken together, these parameters define the regular murein network, which can be visualized as presented in Fig.…”

Visualizing multiple constrictions in spheroidal Escherichia coli cells

“…It has been proposed that planes of successive divisions in spheroidal E. coli cells lie either parallel [29] or perpendicular [30] to each other, restricted to one or two dimensions, respectively. To test the hypothesis that divisions can occur in planes alternating in three dimensions [32], we have recently developed a method to generate spheriodal cells with secondary constrictions during growth in suspension [26].…”

“…The dispute about the relative planes of subsequent divisions in spheroidal E. coli [26,29,30] can be resolved by visualizing the nascent FtsZ rings [31] in such cells. This is the aim of the investigation described here.…”

Perpendicular planes of FtsZ arcs in spheroidal Escherichia coli cells

“…The question whether this stems from a fundamental difference is moot. Cooper [1] presumes that the peptidoglycan 'constrained-hoop' structure of rod-shaped bacteria such as Escherichia coli forces them to divide in one dimension, while Begg and Donachie [2] demonstrated that they could do so in two. We have argued [3] that the rigid peptidoglycan forces the two replicating nucleoids to segregate along cell length and that division ring is placed at the envelope adjacent to and between them, irrespective of the previous location upon termination of a chromosome replication cycle [4].…”