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

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....

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Autores principales: Wu, Xianghao, Altman, Ronni, Eiteman, Mark A, Altman, Elliot
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2013
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3599867/
https://www.ncbi.nlm.nih.gov/pubmed/23360655
http://dx.doi.org/10.1186/1754-1611-7-3
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author Wu, Xianghao
Altman, Ronni
Eiteman, Mark A
Altman, Elliot
author_facet Wu, Xianghao
Altman, Ronni
Eiteman, Mark A
Altman, Elliot
author_sort Wu, Xianghao
collection PubMed
description 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. 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. 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.
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spelling pubmed-35998672013-03-17 Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli Wu, Xianghao Altman, Ronni Eiteman, Mark A Altman, Elliot J Biol Eng Research 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. 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. 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. BioMed Central 2013-01-29 /pmc/articles/PMC3599867/ /pubmed/23360655 http://dx.doi.org/10.1186/1754-1611-7-3 Text en Copyright ©2013 Wu et al; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research
Wu, Xianghao
Altman, Ronni
Eiteman, Mark A
Altman, Elliot
Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title_full Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title_fullStr Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title_full_unstemmed Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title_short Effect of overexpressing nhaA and nhaR on sodium tolerance and lactate production in Escherichia coli
title_sort effect of overexpressing nhaa and nhar on sodium tolerance and lactate production in escherichia coli
topic Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3599867/
https://www.ncbi.nlm.nih.gov/pubmed/23360655
http://dx.doi.org/10.1186/1754-1611-7-3
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