Fate of plasmids containing Mu DNA: chromosome association and mobilization

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Plasmid DNA and chromosomal DNA are distinct genetic entities in bacteria.
• Bacteriophages, like Mu phage, can integrate into or interact with the host chromosome.
• Understanding plasmid-chromosome interactions is crucial for bacterial genetics and gene transfer.

Purpose of the Study:

• To investigate the interaction between plasmid DNA and the bacterial chromosome.
• To determine the conditions and genetic dependencies of plasmid-chromosome association.
• To explore the implications of this association for genetic stability and gene transfer.

Main Methods:

• Utilized cesium chloride (CsCl) density gradients with the fluorescent dye diamidinophenylindole-dihydrochloride (DAPI) for enhanced DNA resolution.
• Examined Proteus mirabilis and Escherichia coli strains carrying RP4::Mucts plasmid.
• Induced prophage and analyzed plasmid DNA association with the chromosome using detergent, RNase, and pronase treatments.
• Conducted genetic studies with F'::mini Mu plasmids.

Main Results:

• Plasmid DNA became quantitatively associated with the bacterial chromosome after thermal induction of Mu prophage.
• This association was resistant to detergent, RNase, and pronase treatments.
• The association was dependent on the expression of Mu genes and correlated with Mu DNA replication.
• Genetic studies revealed that some association events led to stable Hfr formation, independent of Mu gene B.

Conclusions:

• Mu phage induction triggers a stable association between plasmid DNA and the host chromosome.
• This plasmid-chromosome linkage is an active process dependent on Mu gene expression and DNA replication.
• The observed association can result in the formation of stable Hfr strains, indicating a role in bacterial recombination and gene transfer.