Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli

dc.contributor Middle Tennessee State University. Biology Department. en_US
dc.contributor.author Wu, Xianghao en_US
dc.contributor.author Altman, Ronni en_US
dc.contributor.author Eiteman, Mark A en_US
dc.contributor.author Altman, Elliot en_US
dc.date.accessioned 2014-06-24T15:32:02Z
dc.date.available 2014-06-24T15:32:02Z
dc.date.issued 2013-01-25 en_US
dc.description.abstract Background: Like other bacteria, Escherichia coli must carefully regulate the intracellular concentration of sodium ion (Na+). During the bacterial production of any organic acid, cations like Na+ invariably accumulate during a process which must maintain a near neutral pH. In this study, the E. coli nhaA gene encoding the Na+/H+ antiporter membrane protein and the nhaR gene encoding the NhaA regulatory protein were overexpressed in wild-type E. coli MG1655 and in MG1655 pflB (ALS1317) which lacks pyruvate formate lyase activity and thus accumulates lactate under anaerobic conditions. en_US
dc.description.abstract Results: Expression of either the nhaA or nhaR gene on the high copy inducible expression vector pTrc99A caused a significant reduction in the growth rate of MG1655. No change in growth rate was observed for MG1655 or ALS1317 for Na+ concentrations of 0.75-0.90 M when the medium copy pBR322 plasmid was used to overexpress the two genes. In a fed-batch process to produce the model acid lactate with NaOH addition for pH control, lactate accumulation ceased in MG1655, MG1655/pBR322, MG1655/pBR322-nhaR and MG1655/pBR322-nhaA when the concentration reached 55-58 g/L. In an identical process lactate accumulation in MG1655/pBR322-nhaAR did not terminate until the concentration reached over 70 g/L. en_US
dc.description.abstract Conclusions: Although overexpression the genes did not improve growth rate at high Na+ concentrations, the overexpression of nhaA and nhaR together led to a 25% increase in lactate production. Thus, the observed (absence of) impact that these genetic modifications had on growth rate is a poor indicator of their effect on acid accumulation. The overexpression of nhaAR did not cause faster lactate production, but permitted the culture to continue accumulating lactate at 10% greater Na+ concentration. en_US
dc.identifier.citation Journal of Biological Engineering. 2013 Jan 25;7:3 en_US
dc.identifier.uri http://jewlscholar.mtsu.edu/handle/mtsu/4231
dc.rights This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. en_US
dc.subject Sodium tolerance en_US
dc.subject Lactate en_US
dc.subject Lactic acid en_US
dc.subject Fed-batch fermentation en_US
dc.title Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli en_US
dc.type Research Article en_US
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