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Balanced growth of Ecoli MG1655/pTrc99a(NOX+) at different growth rates

ABSTRACT: Responses of Escherichia coli MG1655/pTrc99a(NOX+) grown at different growth rates in chemostat in M9 + salts NOX: NADH oxygenase converts NADH to NAD. Cells with NOX are able to recycle the excess NADH generated during rapid growth, leading to lesser accumulation of acetate Keywords: different growth rates in parallel

ORGANISM(S): Escherichia coli

PROVIDER: GSE4365 | GEO | 2006/03/08

SECONDARY ACCESSION(S): PRJNA94823

REPOSITORIES: GEO

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Project description:Oxidative stress due to endogenous hydrogen peroxide production by Lactobacillus species is a well-known issue in the food industry. In this study, the transcriptional response to oxygen of Lactobacillus johnsonii, one of the H2O2-producing strains used in the food industry, was analyzed. It was found that aerobic growth conditions led to a more than two-fold downregulation of 45 genes as compared to anaerobic growth, whereas 6 genes were more than twofold upregulated. Among the upregulated genes were two genes that displayed significant homology to NADH-dependent oxidoreductase (NOX). The postulated transcriptional regulation of the nox promoter by oxygen was studied using a GUS-reporter construct, confirming a 2.1-fold upregulated GUS-expression upon aerobic growth. Exposure to sublethal levels of hydrogen peroxide did not result in significant regulation of the nox promoter. In a previous study of hydrogen peroxide production by L. johnsonii, a NADH flavin reductase (NFR) was identified to be involved in hydrogen peroxide production. An NFR-deficient derivative was strongly impaired in H2O2 production, but regained a partial H2O2 producing capacity upon prolonged oxygen exposure. The nox-promoter appeared to be 3.6-fold upregulated under aerobic conditions in the NFR-deficient background, which may imply a role of this gene in the regained H2O2 production. Indeed, deletion of the nox-gene in the NFR-deletion background, resulted in a strain that no longer produced H2O2, also during prolonged exposure to oxygen. The double-mutant (nfr, nox) displayed strongly impaired aerobic growth and oxygenation induced rapid growth stagnation that is not caused by H2O2. We conclude that H2O2 production in L. johnsonii is primarily dependent on NFR but can also involve an oxygen-inducible NADH oxidase under aerobic conditions. Moreover, our results imply that H2O2 production plays a prominent role in oxygen tolerance of L. johnsonii. loop design of the samples including two shortcuts

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Balanced growth of Ecoli MG1655/pTrc99a(NOX+) at different growth rates

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