Deletion of the min Operon Results in Increased Thermosensitivity of an ftsZ84 Mutant and Abnormal FtsZ Ring Assembly, Placement, and Disassembly

Abstract

To investigate the interaction between FtsZ and the Min system during cell division of Escherichia coli, we examined the effects of combining a well-known thermosensitive mutation of ftsZ, ftsZ84, with ⌬minCDE, a deletion of the entire min locus. Because the Min system is thought to down-regulate Z-ring assembly, the prediction was that removing minCDE might at least partially suppress the thermosensitivity of ftsZ84, which can form colonies below 42°C but not at or above 42°C. Contrary to expectations, the double mutant was significantly more thermosensitive than the ftsZ84 single mutant. When shifted to the new lower nonpermissive temperature, the double mutant formed long filaments mostly devoid of Z rings, suggesting a likely cause of the increased thermosensitivity. Interestingly, even at 22°C, many Z rings were missing in the double mutant, and the rings that were present were predominantly at the cell poles. Of these, a large number were present only at one pole. These cells exhibited a higher than expected incidence of polar divisions, with a bias toward the newest pole. Moreover, some cells exhibited dramatically elongated septa that stained for FtsZ, suggesting that the double mutant is defective in Z-ring disassembly, and providing a possible mechanism for the polar bias. Thermoresistant suppressors of the double mutant arose that had modestly increased levels of FtsZ84. These cells also exhibited elongated septa and, in addition, produced a high frequency of branched cells. A thermoresistant suppressor of the ftsZ84 single mutant also synthesized more FtsZ84 and produced branched cells. The evidence from this study indicates that removing the Min system exposes and exacerbates the inherent defects of the FtsZ84 protein, resulting in clear septation phenotypes even at low growth temperatures. Increasing levels of FtsZ84 can suppress some, but not all, of these phenotypes.Bacteria such as Escherichia coli normally divide by binary fission, producing two daughter cells of equal size, each containing a nucleoid. The division process starts with the localization of FtsZ to the center of the mother cell and formation of a septal ring structure, the Z ring. Other essential cell division proteins are then recruited to the Z ring, and the ring contracts as the ingrowing septum invaginates. Once the septum is fully formed, the Z ring disappears and the daughter cells separate. Little is known about what regulates Z-ring assembly, contraction, and disassembly.FtsZ is essential for cell division and viability. Deletion or mutation of the ftsZ gene blocks cell division at an early stage, causing the formation of long filamentous cells with multiple nucleoids. The thermosensitive ftsZ84 mutant grows normally at 28°C but becomes filamentous at higher temperatures and fails to form colonies at 42°C. This mutant has been particularly well-studied because it encodes a protein with an amino acid change in a domain implicated in GTP binding. This domain is highly conserved among FtsZ proteins throughout prokaryotes and ...

Physiological consequences associated with overproduction of Mycobacterium tuberculosis FtsZ in mycobacterial hosts

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The Interplay of ClpXP with the Cell Division Machinery in Escherichia coli

“…Branches were not observed in cultures of wild-type cells or any of the strains carrying a single deletion. Branching has previously been observed in cells carrying the minCDE triple deletion under certain conditions and in combination with ftsZ84 (3,39). The number of minicells in all strains carrying the minC deletion was similar (ϳ25%) with respect to the total number of cells in each culture, regardless of length.…”

Genome Sequence of the Chemolithoautotrophic Nitrite-Oxidizing Bacterium Nitrobacter winogradskyi Nb-255

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