Involvement of catalase and superoxide dismutase in hydrophobic organic solvent tolerance of Escherichia coli

Noriyuki Doukyu,Katsuya Taguchi

doi:10.1186/s13568-021-01258-w

Abstract

Escherichia coli strains are generally sensitive to hydrophobic organic solvents such as n-hexane and cyclohexane. Oxidative stress in E. coli by exposure to these hydrophobic organic solvents has been poorly understood. In the present study, we examined organic solvent tolerance and oxygen radical generation in E. coli mutants deficient in reactive oxygen species (ROS)-scavenging enzymes. The organic solvent tolerances in single gene mutants lacking genes encoding superoxide dismutase (sodA, sodB, and sodC), catalase (katE and katG), and alkyl hydroperoxide reductase (ahpCF) were similar to that of parent strain BW25113. We constructed a BW25113-based katE katG double mutant (BW25113∆katE∆katG) and sodA sodB double mutant (BW25113sodA∆sodB). These double-gene mutants were more sensitive to hydrophobic organic solvents than BW25113. In addition, the intracellular ROS levels in E. coli strains increased by the addition of n-hexane or cyclohexane. The ROS levels in BW25113∆katE∆katG and BW25113∆sodA∆sodB induced by exposure to the solvents were higher than that in BW25113. These results suggested that ROS-scavenging enzymes contribute to the maintenance of organic solvent tolerance in E. coli. In addition, the promoter activities of sodA and sodB were significantly increased by exposure to n-hexane.

Highlights

Efficient microbial production of valuable organic compounds including biofuels and fine chemicals from renewable biomass resources is one of the crucial challenges in the establishment of a sustainable society
We investigated the involvement of reactive oxygen species (ROS)-scavenging enzymes in hydrophobic organic solvent-tolerance
It has been reported that a sodA sodB double mutant was much more sensitive to paraquat than the wild type, the absence of only the sodA gene or only the sodB gene had no effect on the sensitivity to paraquat (Carlioz and Touati 1986)

Summary

Introduction

Efficient microbial production of valuable organic compounds including biofuels and fine chemicals from renewable biomass resources is one of the crucial challenges in the establishment of a sustainable society Some of these valuable chemicals such as advanced biofuels and bulk chemicals, including organic solvents including 1-octanol and styrene, are toxic to various microorganisms such as E. coli and Pseudomonas putida (Akhtar et al 2015; Lennen et al 2013; Mukhopadhyay 2015). Various tolerance mechanisms in E. coli strains have been studied with hydrophobic organic solvents such as n-hexane and cyclohexane (Aono 1998) These findings are useful for improving the production of hydrophobic solvents and fatty acids (Akhtar et al 2015; Lennen et al 2013). Little is known about the ROS generation in microbial cells by these hydrophobic organic solvents

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Results

Conclusion