Effect of acidic condition on the metabolic regulation of Escherichia coli and its phoB mutant
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ORIGINAL PAPER
Effect of acidic condition on the metabolic regulation of Escherichia coli and its phoB mutant Lolo Wal Marzan • Chowdhury Mohammad Monirul Hasan Kazuyuki Shimizu
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Received: 25 May 2012 / Revised: 5 December 2012 / Accepted: 6 December 2012 / Published online: 30 December 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract Effect of acidic condition on the fermentation characteristics was investigated by the continuous culture of Escherichia coli. In accordance with down-regulation of crp gene transcript level as well as up-regulation of arcA, the expressions of the TCA cycle genes were down-regulated, which caused more acetate formation at acidic condition under aerobic condition. It was also shown that yfiD was up-regulated in accordance with up-regulation of fnr, and the respiratory pathway genes were up-regulated under acidic condition. The effect of phoB gene knockout on fermentation characteristics was also investigated. Under micro-aerobic condition, the fermentation pattern changed in such a way that formate and lactate were more produced at lower pH due to up-regulations of pflA, yfiD and ldhA genes, whereas ethanol was less produced as compared to the case at neutral pH. The overall regulation mechanism under acidic condition was clarified based on fermentation characteristics and gene transcript levels. Keywords Metabolic regulation at low pH Glutamate decarboxylase Acidic condition phoB mutant
Communicated by Jorge Membrillo-Herna´ndez.
Electronic supplementary material The online version of this article (doi:10.1007/s00203-012-0861-7) contains supplementary material, which is available to authorized users. L. W. Marzan C. M. M. Hasan K. Shimizu (&) Department of Bioscience and Bioinformatics, Kyushu Institute of Technology, Iizuka, Fukuoka 820-8502, Japan e-mail: [email protected] K. Shimizu Institute of Advanced Bioscience, Keio University, Tsuruoka, Yamagata 997-0017, Japan
Introduction Bacteria have a number of strategies for surviving at low pH. In particular, intestinal organisms that colonize and cause diseases in the human gut must have to tolerate an extreme acid challenge. Growth in a moderately acidic environment triggers the synthesis of proteins that protect the cell from acidic condition. Acid resistance, acid tolerance, and acid habituation are used to describe survival at low-pH condition (Bearson et al. 1998). Several acid stress response systems that can protect Escherichia coli from low pH have been identified by several researchers (Richard and Foster 2003, 2004; Sayed and Foster 2009; Stincone et al. 2011). E. coli is a facultative anaerobe that uses transcription factors to control gene expressions in response to the change in the growth environment. Among them, the effect of pH on the metabolism is of practical interest for the variety of applications such as heterologous protein production, simultaneous saccharification and fermentation (SSF), where the culture pH has to be lower in SSF due to enzymatic hydrolysis of cellulose in the fermen
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