Reducing phenotypic instabilities of microbial population during
continuous cultivation based on cell switching dynamics
Abstract
Predicting the fate of a microbial population (i.e., growth, gene
expression…) remains a challenge, especially when this population
is exposed to very dynamic environmental conditions, such as those
encountered during continuous cultivation. Indeed, the dynamic nature of
continuous cultivation process implies the potential deviation of the
microbial population involving genotypic and phenotypic diversification.
This work has been focused on the induction of the arabinose operon in
Escherichia coli as a model system. As a preliminary step, the GFP level
triggered by an arabinose-inducible ParaBAD promoter has been tracked by
flow cytometry in chemostat with glucose-arabinose co-feeding. For a
large range of glucose-arabinose co-feeding, the simultaneous occurrence
of GFP positive and negative subpopulation was observed. In a second set
of experiments, continuous cultivation was performed by adding either
glucose or arabinose, based on the ability of individual cells for
switching from low GFP to high GFP states, according to a technology
called segregostat. In segregostat mode of cultivation, on-line flow
cytometry analysis was used for adjusting the arabinose/glucose
transitions based on the phenotypic switching capabilities of the
microbial population. This strategy allowed finding an appropriate
arabinose pulsing frequency, leading to a prolonged maintenance of the
induction level with limited impact on phenotypic diversity for more
than 60 generations. This result suggests that constraining individual
cells into a given phenotypic trajectory is maybe not the best strategy
for directing cell population. Instead, allowing individual cells
switching around a predefined threshold seems to be a robust strategy
leading to oscillating, but predictable, cell population behavior.