Abstract
Precise temporal and spatial control of cell division is essential for progeny survival. The current general view is that precise positioning of the division site at midcell in rod-shaped bacteria is a result of the combined action of the Min system and nucleoid (chromosome) occlusion. Both systems prevent assembly of the cytokinetic Z ring at inappropriate places in the cell, restricting Z rings to the correct site at midcell. Here we show that in the bacterium Bacillus subtilis Z rings are positioned precisely at midcell in the complete absence of both these systems, revealing the existence of a mechanism independent of Min and nucleoid occlusion that identifies midcell in this organism. We further show that Z ring assembly at midcell is delayed in the absence of Min and Noc proteins, while at the same time FtsZ accumulates at other potential division sites. This suggests that a major role for Min and Noc is to ensure efficient utilization of the midcell division site by preventing Z ring assembly at potential division sites, including the cell poles. Our data lead us to propose a model in which spatial regulation of division in B. subtilis involves identification of the division site at midcell that requires Min and nucleoid occlusion to ensure efficient Z ring assembly there and only there, at the right time in the cell cycle.
Highlights
Mechanisms that regulate cell division in time and space are of fundamental importance to biology because they ensure equal partitioning of DNA into newborn cells
Correct positioning of the division site at the cell centre in rod-shaped bacteria is generally believed to occur via the combined action of two factors: (i) nucleoid occlusion and (ii) a set of proteins known collectively as the Min system
The earliest stage in bacterial cell division is the assembly of a ring, called the Z ring, at the division site
Summary
Mechanisms that regulate cell division in time and space are of fundamental importance to biology because they ensure equal partitioning of DNA into newborn cells. The earliest observable event in cell division in rodshaped bacteria such as Escherichia coli and Bacillus subtilis is the polymerization of the highly conserved tubulin-like protein, FtsZ, to form a contractile structure called the Z ring, at midcell [1,2,3,4,5,6]. The Z ring recruits several division proteins to form the division complex, known as the divisome, to enable cytokinesis. In this way FtsZ acts as a so-called founder protein that recognizes a sub-cellular location, and instructs other proteins to assemble there through a series of protein interactions [7]. The key question concerning the regulation of cell division is what dictates the sub-cellular recruitment of this founder protein, FtsZ, precisely to midcell?
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