Modeling holin function during lambda phage infection of Escherichia coli

Bacteriophage lambda is a virus that infects the bacterium Escherichia coli, terminating its infection cycle with a catastrophic lysis event. Lysis timing is regulated by holins --- small bacteriophage-encoded proteins that accumulate within the host inner membrane during late-protein synthesis after infection and cause lysis of the host cell at a precise genetically programmed time.;The oligomerization of holin proteins to form 'rafts' within the membrane is a central step in holin function. Within the context of our model we investigate the dependence of the raft number distribution on the energized host membrane --- with a focus on the maximum number of rafts expected after cell death.;We review general and lysis-specific phage phenomenology. We then derive an analytic expression for the lysis time distribution based on collective holin properties. We find that an earlier two-stage nucleation model leads to significant asymmetry of the lysis timing distribution, which has not been previously reported. We undertook single-cell studies of bacteriophage lambda induced lysis of E. coli which detailed lysis time distributions for both normal lysis and KCN-induced early lysis. These detailed distributions provide more' precise average lysis time and width, previously characterized with batch cultures, but also the asymmetry of the lysis timing about its mean for the first time. Statistical errors of these moments have also been estimated. With these measures, we constrain the parameters of a quantitative two-stage nucleation model of lysis timing via holin domain nucleation followed by hole nucleation within those domains. We use the lysis asymmetry to estimate the rate of hole formation within condensed holin domains in the bacterial inner membrane. We find that the delay between the time of KCN poisoning and host cell lysis is anomalously large compared to the lysis width, suggesting the existence of a reservoir of holin in the host bacterium that allows the continued addition of active holin to the bulk of the membrane after host cell death. Continued holin addition after host death leads to much earlier lysis upon cell death, and so represents a new back door to lysis for bacteriophage lambda.