The Role of Catalase HPII Levels in Protection against UV-A Damage in a Catalase Knockout Escherichia coli Strain

Abstract

E. coli strains show low sensitivity to ultraviolet-A (UV-A) irradiation, a common method of decontamination. The two known catalases in E. coli, hydroperoxidase I (HPI) and hydroperoxidase II (HPII) are suspected to protect against UV-A inactivation by removing destructive reactive oxygen species (ROS). Catalase HPI knockout UM197 cells, subjected to UV-A, previously showed wildtype survival suggesting that only HPII, encoded by katE, protects against UV-A. However, katE overexpression in catalase double knockout strain UM2 did not protect against UV-A possibly due to the photosensitizing properties of HPII at high concentrations. In this study, a UM197 strain containing antisense katE (a katE ) on the pBAD24 construct, CKLW09W2 cells were differentially induced at mid-log phase to create decreasing HPII levels. The araC promoter on pBAD24 was induced using zero, low, medium, and high L-arabinose concentrations followed by UV-A irradiation of respective bacterial solutions in water. Survival was determined as a percentage of colony counts of control treatments incubated in the dark. Compared to the wildtype plasmid control, uninduced CKLW09W2 cells were twice as susceptible to UV-A killing suggesting negative effects of the a katE insert and/or genetic manipulations conducted to create the strain; addition of L-arabinose did not affect growth rates. At all induction levels, CKLW09W2 survival was similar and HPII expression did not correlate with UV-A survival. Some variations in the data were observed and can be attributed to nutrient deprivation in water, loss of inducibility and/or degradation of a katE mRNA during mid-log phase growth. The overall results of this study indicate that HPII does not provide E. coli protection against UV-A and other gene(s) may be involved.