Single-cell burst size estimates

Bacteriophage burst size is the average number of phage virions released
from infected bacterial cells, and its magnitude depends on the duration
of an intracellular progeny accumulation phase. Burst size is often
measured at the population, not single-cell, level, and consequently,
statistical moments are not commonly available. In this study, we
estimated the bacteriophage lambda (λ) single-cell burst size mean and
variance following different length intracellular accumulation periods by
employing E. coli lysogens bearing lysis-deficient λ prophages. Single
lysogens can be isolated and chemically lysed at desired times following
prophage induction to quantify progeny intracellular accumulation within
individual cells. Our data show that λ phage burst size initially
increased exponentially with increased lysis time (i.e., period between
induction and chemical lysis), and then saturated at longer lysis times.
We also demonstrated that cell-to-cell variation or “noise” in lysis
timing did not contribute significantly to burst size noise. The burst
size noise remained constant with increasing mean burst size. The most
likely explanation for the experimentally observed constant burst size
noise was that cell-to-cell differences in burst size originated from
intercellular heterogeneity in cellular capacities to produce phages. The
mean burst size measured at different lysis times was positively
correlated to cell volume, which may determine the cellular phage
production capacity. However, experiments controlling for cell size
indicated that there are other factors in addition to cell size that
determine this cellular capacity.