Lambda mutants which persist as plasmids

Area of Science:

• Bacteriology
• Molecular Biology
• Virology

Background:

• Lambda phages are viruses that infect bacteria.
• Gene N mutations in lambda phages prevent host cell lysis.
• Lambda phage genomes can exist as plasmids within host bacteria.

Purpose of the Study:

• To investigate the persistence and replication of lambda phage genomes in host bacteria.
• To characterize the behavior of mutated lambda phages that form plasmids.
• To understand the relationship between lambda plasmids and host immunity.

Main Methods:

• Infection of sensitive host bacteria with lambda phages mutated in gene N.
• Analysis of plasmid formation and replication using genetic markers (cI, sus, ts, c).
• Co-infection experiments with multiple phage particles and co-existence with F plasmids.
• Assessment of bacterial immunity and complementation between plasmids and superinfecting phages.

Main Results:

• Lambda phages mutated in gene N do not kill host bacteria but form plasmids.
• Plasmids are formed by various lambda genome mutants, including cI(+), sus, ts, and c.
• Infected bacteria become carriers, with 10-20 lambda plasmids per host genome.
• Lambda and F plasmids replicate independently in co-infected bacteria.
• Lambda plasmid carriers are not immune and exhibit complementation with superinfecting lambda mutants.

Conclusions:

• Lambda phage gene N mutations enable plasmid formation and bacterial carrier states.
• Lambda plasmids replicate autonomously and independently of host F plasmids.
• The absence of immunity in carriers and complementation suggest complex interactions within the host.