Phage N4 uses a SAR endolysin-holin system for host cell lysis

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacteriophages (phages) are viruses that infect bacteria, typically causing host cell lysis to release progeny.
• Lysis inhibition (LIN) is a phenomenon where some phages delay lysis, increasing progeny yield.
• Phages T4 and N4 of Escherichia coli are known to exhibit LIN, but their lysis mechanisms differ.

Purpose of the Study:

• To characterize the phage N4 proteins involved in host cell lysis and lysis inhibition (LIN).
• To define the minimal gene set required for N4 lysis and its sufficiency in inducing LIN.
• To identify genomic regions regulating N4 LIN through comparative analysis of LIN-proficient and deficient mutants.

Main Methods:

• Molecular and genetic characterization of phage N4 lysis proteins.
• Heterologous expression and complementation assays to define gene functions.
• Sequence comparison of wild-type and LIN-deficient mutant phage N4 libraries.

Main Results:

• The minimal gene set required for N4 lysis was defined and shown to be sufficient for inducing LIN under high-density infection.
• Genomic regions within and outside the lysis cassette were identified as involved in N4 LIN.
• A model for the regulation of N4 lysis proteins to induce LIN was proposed.

Conclusions:

• Phage N4 lysis proteins can be regulated to induce lysis inhibition (LIN), despite lacking conservation with phage T4 components.
• Direct modulation of lysis initiation appears to be a common strategy among phages.
• This study provides a foundation for identifying other phages that regulate progeny production numbers via lysis modulation.