The one-step growth curve of bacteriophages is a fundamental concept in virology that allows researchers to study, observe and quantify the viral replication cycle in a controlled environment. A single replication cycle of virus is quantified; therefore called one-step growth curve. This model was first developed by Max Delbrück and Emory Ellis in 1939, using the T4 bacteriophage and Escherichia coli as the host.
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Phases of the One-Step
Growth Curve
The one-step growth
curve consists of three main phases:
1. Latent Period
This is the initial
phase where no new phage particles are detected outside the host cell.
After inoculation, the
phage attaches to the surface of the host bacterium called as adsorption. This
is followed by the injection of genetic material into the host cell
Latent Period can be
further divided into two sub-phases: eclipse phase and Phage Assembly
Eclipse Phase occurs
immediately after the phage enters the host cell. During this time, the phage synthesizes
its genetic material and protein, but no complete virions are formed yet. The
eclipse phase typically lasts from a few minutes to several hours, depending on
the phage.
Intracellular
Accumulation or Assembly: Here, the newly synthesized viral genetic material is
packaged inside the protein coat to from a complete phage particle within the
host cell.
2. Rise Period: Following
the latent period, the rise period begins when the host cell lyses (bursts),
releasing newly formed phage particles into the surrounding medium. This
results in a rapid increase in the number of detectable phage particles.
3. Plateau Period: After
the initial lysis of phages, the number of free phage particles reaches a
plateau. New phages cannot find host bacterium due to lysis of host cells.
What is Burst size?
It is the average
number of phage particles released from a single infected host cell upon lysis.
It is calculated by dividing the number of phages at the plateau by the number
of phages at the end of the latent period.
References
Zhao, J., Zhang, Z.,
Tian, C., Chen, X., Hu, L., Wei, X., ... & Zhao, X. (2019). Characterizing
the biology of lytic bacteriophage vB_EaeM_φEap-3 infecting multidrug-resistant
Enterobacter aerogenes. Frontiers in microbiology, 10, 420.
Kropinski AM. Practical Advice on the One-Step
Growth Curve. Methods Mol Biol. 2018;1681:41-47. doi:
10.1007/978-1-4939-7343-9_3.