What the book of Lambda doesn’t tell us about temperate phages and lysogeny in the real world

• Type of Material: Article
• Authors: Brandon Berryhill, Emory University; Rodrigo Garcia, Emory University; Ingrid C McCall, Emory University; Waqas Chaudhry, Emory University; Marie-Agnes Petit, Université Paris-Saclay; Bruce Levin, Emory University
• Language: English
• Date: 2022-07-18
• Publisher: Cold Spring Harbor Laboratory
• Publication Version: Preprint (Prior to Peer Review)
• Copyright Statement: The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): https://doi.org/10.1101/2022.05.11.491505
• Title of Journal or Parent Work: bioRxiv
• Grant/Funding Information: US National Institutes of General Medical Sciences grant R35 GM 136407 (BRL)
• Keywords: Escherichia coli; population biology; temperate phage; antibiotics; bacteriophage
• Research Categories: Health Sciences, Pathology; Biology, Microbiology

Abstract

The most significant difference between bacteriophages functionally and ecologically is whether they are purely lytic (virulent) or temperate. Virulent phages can only be transmitted horizontally by infection, most commonly with the death of their hosts. Temperate phages can also be transmitted horizontally, but upon infection of susceptible bacteria, their genomes can be incorporated into that of their host’s as a prophage and be transmitted vertically in the course of cell division by their lysogenic hosts. From what we know from studies with the temperate phage Lambda and other temperate phages, in laboratory culture, lysogenic bacteria are protected from killing by the phage coded for by their prophage by immunity; where upon infecting lysogens, the free temperate phage coded by their prophage are lost. Why are lysogens not also resistant as well as immune to the phage coded by their prophage since immunity does not confer protection against virulent phages? To address this question, we used a mathematical model and performed experiments with temperate and virulent mutants of the phage Lambda in laboratory culture. Our models predict and experiments confirm that selection would favor the evolution of resistant as well as immune lysogens, particularly if the environment includes virulent phage that share the same receptors as the temperate. To explore the validity and generality of this prediction, we examined ten lysogenic Escherichia coli from natural populations. All ten were capable of forming immune lysogens but their original hosts were resistant to the phage coded by their prophage.