DNA packaging by the Bacillus subtilis defective bacteriophage PBSX

Area of Science:

• Molecular Biology
• Microbiology
• Virology

Background:

• Bacteriophage PBSX is a defective phage integrated into Bacillus subtilis 168 chromosomes.
• Mitomycin C induces phage activity and DNA packaging in Bacillus subtilis.

Purpose of the Study:

• To investigate the physical process of DNA packaging by bacteriophage PBSX.
• To determine if PBSX exhibits selectivity in packaging chromosomal and plasmid DNA.
• To understand the role of the prophage region in mitomycin C-induced plasmid alterations.

Main Methods:

• Utilized mitomycin C induction in Bacillus subtilis strains.
• Employed genetically engineered strains with chromosomal genetic flags.
• Analyzed DNA packaging using DNase I resistance assays.
• Examined plasmid DNA structure and replication dynamics.

Main Results:

• Wild-type PBSX packages discrete 13-kilobase DNA fragments via a DNase I-resistant, head-filling mechanism.
• No significant selectivity was observed for packaging specific chromosomal regions.
• Mitomycin C induced increased size and packaging of plasmid DNA in wild-type strains.
• Plasmid replication alterations and subsequent packaging occurred in a strain lacking parts of the PBSX prophage.

Conclusions:

• Bacteriophage PBSX packaging is a size-limited process involving host DNA.
• Mitomycin C induction can lead to the 'cannibalization' of plasmid replication for phage packaging.
• The PBSX prophage region plays a role in mediating mitomycin C-induced plasmid alterations.