Cell growth in escherichia coli study of fluctuations and asymmetry in cell extension

Abstract

Cell dimensions are defined for each species Several cellular pathways guarantee faithful duplication of cell during binary fission However phenotypic heterogeneity has been observed in genetically homogenous populations Advanced scientific studies have proved such fluctuations crucial in the development for they have been associated with phenomena like division of labour and rise of survivors under harsh environmental situations Thesis provides an insight into possible mechanisms for the origin of variations in cell lengths of clonal E coli populations Series of experiments helped assess an elongation in Escherichia coli cells and its effect on the population length distributions In our studies with E coli batch cultures we observed a linear increase in cell length variation above growth rate 1 generation per hour On the other hand below this threshold phenotypic heterogeneity was observed to be reduced but it stayed almost constant for all the growth rates 8216 The point of inflection 8217 in the cell length variation was identified and correspond to the growth rate at which multi fork replication is triggered in a bacterial cell Molecular analysis of RecA dynamics showed increased occurrence of replication fork stalling events at high growth rates We inferred that stochastic arrest in the replication increases multiplicatively at higher growth rates because of multi fork replication in E coli cell which in turn increases the probable halts in cell division through SOS response producing non genetic cell length variation in an isogenic population Deviation from defined cell dimensions has previously been assigned to the fluctuations in gene expression Ergo next step was to probe the effect of replication stochsticity on genetic expression and connect it with phenotypic noise in isogenic populations of E coli MG22 By examining hydroxyurea treated populations at different growth rates we detected that the total gene expression noise can be modulated by the population growth rate Growth rate newline newline