The antioxidant protein PntA coordinates with OmpW to resist oxidant stress in Actinobacillus pleuropneumoniae

Abstract

Bacteria have evolved various strategies to combat oxidative stress caused by reactive oxygen species (ROS). Outer membrane proteins including OmpW play multiple roles in bacterial physiology, stress responses and virulence. In this study, the OmpW protein of Actinobacillus pleuropneumoniae, an important porcine respiratory tract pathogen, was found to contribute to virulence but concurrently to reduce resistance to oxidative stress. An ompW deletion (ΔompW) showed attenuation in mice, and decreased adherence to pig tracheal epithelial cells and resistance to hyperosmotic stress, compared to the wild-type (WT) strain. However, the ΔompW strain exhibited increased resistance to H₂O₂, enhanced survival ability within macrophages, and lower intracellular ROS level. OmpW may serve as a H₂O₂ channel. Further study showed that exposure to H₂O₂ significantly suppressed ompW transcription in the WT strain. Overexpression of these two proteins in WT and ΔompW increased the antioxidative properties of the bacteria. Furthermore, by construction of the double gene mutant ΔompWΔpntA, it was found that PntA could reverse the effects of OmpW on the bacterial survivability and intracellular ROS level after H₂O₂ treatment. Therefore, by interacting with OmpW, PntA alleviated the increased oxidative stress sensitivity caused by OmpW. These results suggest a mechanism whereby antioxidant proteins collaborate with OMPs to protect bacteria from oxidative stress.