Open AccessIncreased Mutation Frequency in Redox-Impaired Escherichia coli Due to RelA- and RpoS-Mediated Repression of DNA Repair
Author(s) -
Amarjeet Singh,
Anis Karimpour-Fard,
Ryan T. Gill
Publication year - 2010
Publication title -
applied and environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.552
H-Index - 324
eISSN - 1070-6291
pISSN - 0099-2240
DOI - 10.1128/aem.00583-10
Subject(s) - rpos , escherichia coli , psychological repression , dna repair , mutation , dna , reversion , dna damage , biology , mutation frequency , genetics , sos response , chemistry , microbiology and biotechnology , gene , phenotype , gene expression , promoter
Balancing of reducing equivalents is a fundamental issue in bacterial metabolism and metabolic engineering. Mutations in the key metabolic genesldhA andpflB ofEscherichia coli are known to stall anaerobic growth and fermentation due to a buildup of intracellular NADH. We observed that the rate of spontaneous mutation inE. coli BW25113 (ΔldhA ΔpflB ) was an order of magnitude higher than that in wild-type (WT)E. coli BW25113. We hypothesized that the increased mutation frequency was due to an increased NADH/NAD+ ratio in this strain. Using several redox-impaired strains ofE. coli and different redox conditions, we confirmed a significant correlation (P < 0.01) between intracellular-NADH/NAD+ ratio and mutation frequency. To identify the genetic basis for this relationship, whole-genome transcriptional profiles were compared between BW25113 WT and BW25113 (ΔldhA ΔpflB ). This analysis revealed that the genes involved in DNA repair were expressed at significantly lower levels in BW25113 (ΔldhA ΔpflB ). Direct measurements of the extent of DNA repair in BW25113 (ΔldhA ΔpflB ) subjected to UV exposure confirmed that DNA repair was inhibited. To identify a direct link between DNA repair and intracellular-redox ratio, the stringent-response-regulatory generelA and the global-stress-response-regulatory generpoS were deleted. In both cases, the mutation frequencies were restored to BW25113 WT levels.