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Updated: Oct 2, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
Chromosome loss from par mutants of Pseudomonas putida depends on growth medium and phase of growth
Richard A Lewis1, Colin R Bignell1, Wei Zeng1
1School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK1.
Abstract:
The proteins encoded by chromosomal homologues of the parA and parB genes of many bacterial plasmids have been implicated in chromosome partitioning. Unlike their plasmid counterparts, mutant phenotypes produced by deleting these genes have so far been elusive or weakly expressed, except during sporulation. Here the properties of Pseudomonas putida strains with mutations in parA and parB are described. These mutants do not give rise to elevated levels of anucleate bacteria when grown in rich medium under standard conditions. However, in M9-minimal medium different parA and parB mutations gave between 5 and 10% anucleate cells during the transition from exponential phase to stationary phase. Comparison of the DNA content of bacteria at different stages of the growth curve, in batch culture in L-broth and in M9-minimal medium, suggests that the par genes are particularly important for chromosome partitioning when cell division reduces the chromosome copy number per cell from two to one. This transition occurs in P. putida during the entry into stationary phase in M9-minimal medium, but not in L-broth. It is proposed that the partition apparatus is important to ensure proper chromosome segregation primarily when the bacteria are undergoing cell division in the absence of ongoing DNA replication.
Insights
Bacterial parA and parB gene mutations cause chromosome partitioning defects, leading to anucleate cells, especially during nutrient-limited growth transitions. These findings highlight the par genes
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacterial plasmid parA and parB genes are known to be involved in chromosome partitioning.
- Mutant phenotypes for chromosomal homologues of these genes are often weak or elusive, except during sporulation.
Purpose of the Study:
- To investigate the properties of Pseudomonas putida strains with mutations in parA and parB.
- To understand the role of these genes in chromosome partitioning under different growth conditions.
Main Methods:
- Generating and characterizing Pseudomonas putida strains with parA and parB mutations.
- Assessing the percentage of anucleate cells under rich (L-broth) and minimal (M9) medium conditions.
- Analyzing bacterial DNA content across different growth phases.
Main Results:
- Mutations in parA and parB did not significantly increase anucleate cells in rich medium.
- In M9-minimal medium, parA and parB mutations resulted in 5-10% anucleate cells during the transition to stationary phase.
- Chromosome partitioning defects were most pronounced when cell division reduced chromosome copy number from two to one, particularly during entry into stationary phase in M9 medium.
Conclusions:
- The parA and parB genes are crucial for chromosome partitioning in P. putida, especially under nutrient-limiting conditions.
- These genes play a vital role during the transition from exponential to stationary phase when DNA replication may not be active.
- The partition apparatus is essential for ensuring proper chromosome segregation during cell division when the chromosome copy number per cell decreases.
