Dynamic fluctuations in a bacterial metabolic network.

The operation of the central metabolism is typically assumed to be deterministic, but dynamics and high connectivity of the metabolic network make it potentially prone to generating fluctuations. However, time-resolved measurements of metabolite levels in individual cells that are required to characterize such fluctuations remained a challenge, particularly in small bacterial cells. Here we use single-cell metabolite measurements based on Förster resonance energy transfer, combined with computer simulations, to explore the real-time dynamics of the metabolic network of Escherichia coli. We observe that steplike exposure of starved E. coli to glycolytic carbon sources elicits large periodic fluctuations in the intracellular concentration of pyruvate in individual cells. These fluctuations are consistent with predicted oscillatory dynamics of E. coli metabolic network, and they are primarily controlled by biochemical reactions around the pyruvate node. Our results further indicate that fluctuations in glycolysis propagate to other cellular processes, possibly leading to temporal heterogeneity of cellular states within a population.

Effect of global transcriptional regulators on kinetic behavior of Escherichia coli under anaerobic fermentation conditions.

The phenotype of Escherichia coli is governed by global transcriptional regulators under variable environmental conditions. Fnr, ArcA, IhfA-B, Crp, and Fis are amongst the major global transcription regulators that change their activity across the range of aeration, hence forming the core transcriptional network responsible for survival under changing aeration conditions. Effect of deletion of these global transcription factors on the kinetics of cell growth and mixed acid production under anaerobic fermentation conditions has not been characterized. To quantify the kinetic parameters in the absence of global transcription factors, experiments were performed using single deletion mutants of the above-mentioned global transcription regulators. The absence of global transcription regulators resulted in a relatively higher glucose uptake rate than that required for the observed growth rate. This further resulted in a higher yield of mixed acids per unit biomass in mutants as compared to the parent strain (E. coli BW25113). Thus, the increased channeling of carbon towards mixed acid secretion resulted in a lower growth rate in the mutants.

The effect of global transcriptional regulators on the anaerobic fermentative metabolism of Escherichia coli.

Global transcription factors are known to regulate the anaerobic growth of Escherichia coli on glucose. These transcription factors help the organism to sense oxygen and accordingly regulate the synthesis of mixed acid producing enzymes. Five global transcription factors, namely ArcA, Fnr, IhfA-B, Crp and Fis, are known to play an important role in the growth phenotype of the organism in the transition from anaerobic to aerobic conditions. The effect of deletion of most of these global transcription factors on the growth phenotype has not been characterized under strict anaerobic fermentation conditions. In order to enumerate the role of global transcription factors in central carbon metabolism, experiments were performed using single deletion mutants of the above mentioned global transcription regulators. The mutants demonstrated lower growth rates, ranging from 3-75% lower growth as compared to the wild-type strain along with varying glucose uptake rates. Global transcription regulators help in lowering formate and acetate synthesis, thereby effectively channeling the carbon towards redox balance (through ethanol formation) and biomass synthesis. Flux analysis of mutant strains indicated that deletion of a single transcription factor alone does not play a significant role in the normalized flux distribution of the central carbon metabolism.