1 research outputs found
Individuality and universality in the growth-division laws of single E. coli cells
The mean size of exponentially dividing E. coli cells cultured in different
nutrient conditions is known to depend on the mean growth rate only. However,
the joint fluctuations relating cell size, doubling time and individual growth
rate are only starting to be characterized. Recent studies in bacteria (i)
revealed the near constancy of the size extension in a single cell cycle (adder
mechanism), and (ii) reported a universal trend where the spread in both size
and doubling times is a linear function of the population means of these
variables. Here, we combine experiments and theory and use scaling concepts to
elucidate the constraints posed by the second observation on the division
control mechanism and on the joint fluctuations of sizes and doubling times. We
found that scaling relations based on the means both collapse size and
doubling-time distributions across different conditions, and explain how the
shape of their joint fluctuations deviates from the means. Our data on these
joint fluctuations highlight the importance of cell individuality: single cells
do not follow the dependence observed for the means between size and either
growth rate or inverse doubling time. Our calculations show that these results
emerge from a broad class of division control mechanisms (including the adder
mechanism as a particular case) requiring a certain scaling form of the
so-called "division hazard rate function", which defines the probability rate
of dividing as a function of measurable parameters. This gives a rationale for
the universal body-size distributions observed in microbial ecosystems across
many microbial species, presumably dividing with multiple mechanisms.
Additionally, our experiments show a crossover between fast and slow growth in
the relation between individual-cell growth rate and division time, which can
be understood in terms of different regimes of genome replication control