Q.83 The doubling time of Escherichia coli is 30 minutes in a culture medium
containing glucose and yeast extract. Phage T7 has a life cycle of 20 minutes
and a burst size of 200 phage per infected E. coli cell. Phage absorption is
instantaneous and occurs at 1 multiplicity of infection (MOI). Bacteria infected
with multiple or single phage give the same burst. 5000 plaque forming units
of T7 phage are added to a culture of 2 × 107 E. coli cells.
Assuming normal division, the E. coli culture will lyse completely by _____ full
cycles of bacterial division.
(Answer in integer)
The Escherichia coli culture will lyse completely by 3 full cycles of bacterial division.
This calculation models the interaction between E. coli growth and T7 phage infection under the given parameters: 30-minute doubling time, 20-minute phage life cycle, 200 burst size, instantaneous absorption at 1 MOI, and initial conditions of 2 × 10^7 cells and 5000 PFUs. The key is tracking uninfected bacteria lineages over discrete 30-minute cycles, as phage infection propagates faster than bacterial division.
Initial Setup
At t=0, 5000 bacteria are instantly infected (MOI=1), leaving 1.995 × 10^7 uninfected. Infected cells lyse after 20 minutes, releasing 5000 × 200 = 1 × 10^6 new phages. These phages immediately infect 1 × 10^6 uninfected cells (assuming excess uninfected bacteria), creating a new infected cohort.
Cycle-by-Cycle Breakdown
Bacterial division occurs synchronously every 30 minutes for uninfected cells; infected cells do not divide but lyse per phage cycle.
- Cycle 0 (t=0 to 30 min): Cohort A (5000 infected) lyses at 20 min, releasing 1 × 10^6 phages infecting cohort B. Uninfected double to 3.99 × 10^7 by 30 min (0.995 × 10^7 remain uninfected post-new infections).
- Cycle 1 (t=30 to 60 min): Cohort B lyses at t=40 min (20 min post-infection), releasing 2 × 10^8 phages, infecting cohort C. Uninfected double to 1.99 × 10^7 by 60 min.
- Cycle 2 (t=60 to 90 min): Cohort C lyses at t=80 min (20 min post-infection), releasing 4 × 10^10 phages—far exceeding remaining 1.99 × 10^7 uninfected cells. All remaining bacteria get infected.
- Cycle 3 (t=90 min): No uninfected left to double; all lineages lyse by t=100 min (cohort C lysis). The culture is fully lysed by end of cycle 3.
Phage progeny grow exponentially (5000 → 10^6 → 2×10^8 → 4×10^10), overwhelming bacteria despite doubling.
Introduction to E. coli T7 Phage Doubling Time Problem
In biotechnology and microbiology exams like CSIR NET, problems on Escherichia coli lysis by T7 phage test exponential growth dynamics. With E. coli doubling time of 30 minutes, T7 phage life cycle of 20 minutes, and burst size of 200, adding 5000 PFUs to 2×10^7 cells at MOI=1 reveals complete lysis by 3 full cycles. This T7 phage infection calculation highlights phage superiority over host division.
Key Parameters Explained
- Doubling time (30 min): Uninfected E. coli divide every 30 min.
- Phage life cycle (20 min): From infection to lysis.
- Burst size (200): Progeny per cell; matches literature.
- Instantaneous absorption ensures precise tracking. Multiple/single phage infections yield same burst.
Step-by-Step Lysis Calculation
Track uninfected over 30-min cycles (normal division benchmark):
| Cycle | Time (min) | Uninfected (×10^7) | New Phages Released | Infected Cohort |
|---|---|---|---|---|
| 0 | 0-30 | 1.995 → 3.99 (double) | 10^6 (cohort A) | B: 10^6 |
| 1 | 30-60 | 0.995 → 1.99 | 2×10^8 (cohort B) | C: 1.99×10^7 |
| 2 | 60-90 | 0 → 0 | 4×10^10 (cohort C) | All lysed |
| 3 | 90+ | 0 | – | Complete lysis |
Phages amplify 40-fold per 30 min vs. bacteria’s 2-fold, clearing all by cycle 3.
CSIR NET Relevance and Tips
Ideal for molecular biology, phage therapy sections. No options given—direct integer answer: 3. Simulate via spreadsheets for variants. Real T7 burst ~100-200 confirms model.
🔑 Primary Keywords:
escherichia coli t7 phage doubling time, phage burst size calculation, e coli lysis cycles, moi 1 infection dynamics
Practice similar phage-bacteria dynamics problems. Answer: 3 full cycles
