Induction of the Lambda Lysogen

 

Tested Studies in Laboratory Teaching, 2013, Volume 34

Lynley Doonan & Carrie Doonan

Abstract

In this experiment, students will examine gene regulation in bacteria – the production of λ phage particles that occurs when the lysogenic relationship between a bacterial cell and its quiescent prophage is disrupted. The lysogenic state in the bacterial cell is maintained by a repressor protein specified by the λ virus; deactivation of the repressor results in de-repression of the regulated genes and production of λ phage. Normally, the lysogenic state is indefinitely stable once established and a lysogenic bacterial cell produces lysogenic progeny cells, but no free viruses. The particular strain of lambda we are using in this experiment has a temperature sensitive mutation (857) in the repressor gene (cI) that results in an altered repressor protein that can be inactivated by a shift to 42o C. Therefore, we can easily initiate the lytic or reproductive cycle of phage lambda in an entire population of lysogenic bacteria and follow the events of phage production. Students are given a lysogenic culture of CM58 bacterial cells that they will shift to 42o C. They will take aliquots of the culture after de-repression and measure the production of lambda phage particles by pour plating with E. coli C600 host cells on agar plates. The phage produced will kill the host bacteria and form a clear area called a plaque upon infection of the host cells. Students will observe the lysis of the lysogenic culture, and the production of lambda phage after de-repression.

Keywords:  induction, Lamda phage, E.coli, lysogenic, pour plating, repressor protein

University of North Carolina, Chapel Hill (2012)