Effects of overproduction of superoxide dismutase on the toxicity of paraquat toward Escherichia coli

S.I Liochev,I Fridovich

doi:10.1016/s0021-9258(18)31509-6

Abstract

Gross overproduction of the manganese-containing superoxide dismutase in Escherichia coli, by virtue of a multicopy plasmid bearing the sodA gene, decreases enumeration on paraquat-containing agar plates. This reflects growth inhibition, not lethality, since cells on these plates can be rescued by exclusion of dioxygen. Growth in liquid medium revealed that the control strain adapted to growth in the presence of paraquat more rapidly than did the overproducer. Glucose-6-phosphate dehydrogenase, taken as a representative of the superoxide-inducible soxR regulon, was induced during exposure to paraquat to a much greater extent in the control than in the superoxide dismutase-over-producing strain. These results support the view that overproduction of superoxide dismutase interferes with induction of the soxR regulon and thus prevents a balanced adaptation to the multiple aspects of the toxicity of aerobic paraquat.

Highlights

Gross overproduction of the manganese-containing duction of superoxide dismutase imposesadeficitin the superoxide dismutase in Escherichia coli,by virtue of induction of glucose-6-phosphate dehydrogenase, whichlikely a multicopy plasmidbearing the sodA gene, decreases mirrors similar deficits in the induction of other products of enumeration on paraquat-containing agar plates
Phosphate dehydrogenase, taken asa representative of Bacterial Strains-Escherichia coli K12 strains carrying the control the superoxide-inducible soxR regulon, was induced during exposure to paraquat to a much greater extent in the control than in the superoxide dismutase-overproducing strain. These results support the view that overproduction of superoxide dismutase interferes with induction of the soxR regulon and prevents a balanced adaptation to the multiple aspects of the plasmid (DKJpHC 79) and thesodA-bearing plasmid (DKl/pDT 1.5) were created and characterizedby Touati [15]
Growth of colonies on agar plates was done as described by Bloch and Ausubel [11].Overnight cultures were diluted 4-fold with fresh medium and were incubated

Summary

Introduction

Gross overproduction of the manganese-containing duction of superoxide dismutase imposesadeficitin the superoxide dismutase in Escherichia coli,by virtue of induction of glucose-6-phosphate dehydrogenase, whichlikely a multicopy plasmidbearing the sodA gene, decreases mirrors similar deficits in the induction of other products of enumeration on paraquat-containing agar plates This the soxR [13, 14] regulon. MATERIALSANDMETHODS phosphate dehydrogenase, taken asa representative of Bacterial Strains-Escherichia coli K12 strains carrying the control the superoxide-inducible soxR regulon, was induced during exposure to paraquat to a much greater extent in the control than in the superoxide dismutase-overproducing strain These results support the view that overproduction of superoxide dismutase interferes with induction of the soxR regulon and prevents a balanced adaptation to the multiple aspects of the plasmid (DKJpHC 79) and thesodA-bearing plasmid (DKl/pDT 1.5) were created and characterizedby Touati [15]. When extracts were to be assayed for enzymatic activitiesc,ells were these agents [1,2,3,4].The dioxygen-dependent phenotypic ab- collected after 6 h of growth and, after washing with cold 50 mM normalities associated with mutational defects in the superoxide dismutase genes and their eliminatiobny reintroduction of a functional superoxide dismutase gene alsoeloquently support thisposition [4,5,6,7,8,9,10]

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Findings

Conclusion