FtsZ rings in mukB mutants with or without the Min system
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Updated: Jul 17, 2026
Gene-targeted Random Mutagenesis to Select Heterochromatin-destabilizing Proteasome Mutants in Fission Yeast
Published on: May 15, 2018
1Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston 77030, USA.
Abstract:
The site of cell division in Escherichia coli is defined by formation of the Z ring between the two segregated daughter nucleoids. Positioning of the Z ring, composed of the highly conserved and tubulin-like FtsZ protein, appears to be negatively regulated by both the nucleoid and the oscillating MinCD inhibitor proteins. MukB protein is probably involved in nucleoid condensation, and in the absence of MukB, the negative effect of the nucleoid on Z rings appears to be partially suppressed. In this study, we examined the localization of Z rings in cells lacking both the Min system and MukB. In the Deltamin DeltamukB double null mutant, essentially all nucleoid-free zones, either at the cell poles or at non-polar sites between nucleoids, contained Z rings. However, a significant proportion of Z rings also formed on top of nucleoids. Interestingly, Z ring clusters often formed at gaps between nucleoids, and some of the rings within the clusters were clearly positioned on top of nucleoids. These results provide further evidence that the negative topological effect of nucleoids in cells lacking MukB is partially but not totally suppressed, and that the absence of the Min system allows more promiscuous Z ring formation.
Insights
In Escherichia coli, cell division relies on the Z-ring. Removing Min system and MukB proteins allows Z-rings to form more freely, even on nucleoids, indicating partial suppression of nucleoid-mediated inhibition.
Area of Science:
- Microbiology
- Cell Biology
- Bacterial Cytokinesis
Background:
- Cell division in Escherichia coli is precisely regulated by the spatial positioning of the Z-ring, primarily composed of FtsZ.
- Z-ring formation is negatively influenced by both the bacterial nucleoid and the Min system (MinC, MinD, MinE).
- MukB protein plays a role in nucleoid condensation, and its absence partially alleviates nucleoid-based Z-ring inhibition.
Purpose of the Study:
- To investigate the localization of Z-rings in Escherichia coli cells lacking both the Min system and MukB protein.
- To understand the combined effects of Min system absence and MukB deficiency on Z-ring placement.
- To further elucidate the regulatory mechanisms governing bacterial cell division site selection.
Main Methods:
- Generating a double null mutant (Deltamin DeltamukB) in Escherichia coli.
- Microscopic analysis to observe and quantify Z-ring localization relative to nucleoids and cell poles.
- Comparative analysis of Z-ring distribution in wild-type, single, and double mutant strains.
Main Results:
- In Deltamin DeltamukB cells, Z-rings formed in most nucleoid-free zones, including cell poles and inter-nucleoid regions.
- A substantial percentage of Z-rings were observed forming directly on top of nucleoids.
- Z-ring clusters frequently appeared in the gaps between nucleoids, with some rings within these clusters located on nucleoids.
Conclusions:
- The absence of MukB partially suppresses the inhibitory effect of nucleoids on Z-ring formation, but this suppression is not complete.
- Eliminating the Min system leads to more widespread and less restricted Z-ring formation.
- These findings highlight the complex interplay between nucleoid organization, Min system, and MukB in ensuring accurate cell division placement in Escherichia coli.
