Data from: Threshold effect of growth rate on population variability of Escherichia coli cell lengths

A long-standing question in biology is the effect of growth on cell size.
Here, we estimate the effect of Escherichia coli growth rate (r) on
population cell size distributions by estimating the coefficient of
variation of cell lengths (CVL) from image analysis of fixed cells in DIC
microscopy. We find that the CVL is constant at growth rates less than one
division per hour, whereas above this threshold, CVL increases with an
increase in the growth rate. We hypothesize that stochastic inhibition of
cell division owing to replication stalling by a RecA-dependent mechanism,
combined with the growth rate threshold of multi-fork replication
(according to Cooper and Helmstetter), could form the basis of such a
threshold effect. We proceed to test our hypothesis by increasing the
frequency of stochastic stalling of replication forks with hydroxyurea
(HU) treatment and find that cell length variability increases only when
the growth rate exceeds this threshold. The population effect is also
reproduced in single-cell studies using agar-pad cultures and ‘mother
machine’-based experiments to achieve synchrony. To test the role of RecA,
critical for the repair of stalled replication forks, we examine the CVL
of E. coli ΔrecA cells. We find cell length variability in the mutant to
be greater than wild-type, a phenotype that is rescued by plasmid-based
RecA expression. Additionally, we find that RecA-GFP protein recruitment
to nucleoids is more frequent at growth rates exceeding the growth rate
threshold and is further enhanced on HU treatment. Thus, we find growth
rates greater than a threshold result in increased E. coli cell lengths in
the population, and this effect is, at least in part, mediated by RecA
recruitment to the nucleoid and stochastic inhibition of division.