Adaptive Responses in the Metabolism of &lt;i&gt;Escherichia coli&lt;/i&gt; in View of Gene Expressions under Aerobic and Micro-aerobic Condition

Br Gen Md Saidur Rahman,Farhana Nasrin,Chowdhury Mohammad Monirul Hasan,Dr Abul Kalam Azad,Mohammad Rashedul Hasan,Dr Md Maruful Kader

doi:10.12691/ajmr-7-3-4

Adaptive Responses in the Metabolism of <i>Escherichia coli</i> in View of Gene Expressions under Aerobic and Micro-aerobic Condition

Br Gen Md Saidur Rahman, Farhana Nasrin + Show 4 more

Open Access

https://doi.org/10.12691/ajmr-7-3-4

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Abstract

The major aims of biology to understanding life at a systems level. Escherichia coli is a metabolically versatile bacterium able to respond to changes in environmental factors availability. The effect of pH downshift on fermentation characteristics was investigated in a continuous culture of Escherichia coli at aerobic and micro-aerobic conditions. Regardless of oxygen availability, higher levels of acetate were associated with lower biomass yields and lower glucose consumption rates at pH 5.5 as compared to the observations made at pH 7.0. Observed gene expressions indicated that the down- regulation of the glucose uptake rate corresponded to the down-regulation of ptsG gene expression which in turn was caused by the up-regulation of mlc gene under the positive control of Crp. In accordance with up-regulation of arcA gene expression at acidic conditions, the expressions of TCA cycle-related genes such as icdA and gltA, and the respiratory chain gene cyoA were down-regulated, whereas cydB gene expression was up-regulated. Decreased activity of the TCA cycle caused more acetate formation at lower pH levels. Under micro-aerobic condition, higher levels of formate and lactate were produced at lower pH due to up-regulation of pflA, yfiD and ldhA genes. Meanwhile, lower levels of ethanol were produced due to the down-regulation of adhE gene at lower pH, as compared to the observation at neutral pH. The combined effect of pH and temperature on gene expression was also investigated and observed that decreases in the specific glucose consumption rate were associated with increases in the specific acetate production rate. This type of information is useful for the production of recombinant proteins, bio-molecules, simultaneous saccharification and fermentation (SSF) and strain improvement.

Highlights

The ability of bacterium to respond rapidly and effectively to environmental perturbation is a distinguishing and vital aspect of their physiology
We investigated metabolism changes in E. coli at low pH with respect to gene expressions under aerobic and micro-aerobic conditions
To clarify the phenomenon of E. coli metabolism under low pH, gene expressions were measured by RT-PCR

Summary

Introduction

The ability of bacterium to respond rapidly and effectively to environmental perturbation is a distinguishing and vital aspect of their physiology. The molecular toolbox, enabling genetic engineering and studying of regulation and gene expression, is presumably the largest that exists for one particular organism [1]. Most acid tolerance systems are activated at the late growth phase and/or the stationary phase, acid tolerance is observed in the exponential growth phase of E. coli under aerobic conditions and this is advantageous from the productivity point of view. Some of these acid resistance systems depend on the available extracellular amino acids such as glutamate, arginine and lysine.

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