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Abstract
The quantitative study of the cell growth has led to many fundamental insights in
our understanding of a wide range of subjects, from the cell cycle to senescence.
Of particular importance is the growth rate, whose constancy represents a physiological
steady state of an organism. Recent studies, however, suggest that the rate of elongation
during exponential growth of bacterial cells decreases cumulatively with replicative
age for both asymmetrically and symmetrically dividing organisms, implying that a
"steady-state" population consists of individual cells that are never in a steady
state of growth. To resolve this seeming paradoxical observation, we studied the long-term
growth and division patterns of Escherichia coli cells by employing a microfluidic
device designed to follow steady-state growth and division of a large number of cells
at a defined reproductive age. Our analysis of approximately 10(5) individual cells
reveals a remarkable stability of growth whereby the mother cell inherits the same
pole for hundreds of generations. We further show that death of E. coli is not purely
stochastic but is the result of accumulating damages. We conclude that E. coli, unlike
all other aging model systems studied to date, has a robust mechanism of growth that
is decoupled from cell death.
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