Identification of FtpA, a Dps-Like Protein Involved in Anti-Oxidative Stress and Virulence in Actinobacillus pleuropneumoniae.

Bacteria have evolved a variety of enzymes to eliminate endogenous or host-derived oxidative stress factors. The Dps protein, first identified in Escherichia coli, contains a ferroxidase center, and protects bacteria from reactive oxygen species damage. Little is known of the role of Dps-like proteins in bacterial pathogenesis. Actinobacillus pleuropneumoniae causes pleuropneumonia, a respiratory disease of swine. The A. pleuropneumoniae gene is upregulated during shifts to anaerobiosis, in biofilms and, as found in this study, in the presence of HO. An A. pleuropneumoniae deletion mutant (Δ) had increased HO sensitivity, decreased intracellular viability in macrophages, and decreased virulence in a mouse infection model. Expression of in an E. coli mutant restored wild-type HO resistance. FtpA possesses a conserved ferritin domain containing a ferroxidase site. Recombinant rFtpA bound and oxidized Fe reversibly. Under aerobic conditions, the viability of an Δ mutant was reduced compared with the wild-type strain after extended culture, upon transition from anaerobic to aerobic conditions, and upon supplementation with Fenton reaction substrates. Under anaerobic conditions, the addition of HO resulted in a more severe growth defect of Δ than it did under aerobic conditions. Therefore, by oxidizing and mineralizing Fe, FtpA alleviates the oxidative damage mediated by intracellular Fenton reactions. Furthermore, by mutational analysis, two residues were confirmed to be critical for Fe binding and oxidization, as well as for A. pleuropneumoniae HO resistance. Taken together, the results of this study demonstrate that A. pleuropneumoniae FtpA is a Dps-like protein, playing critical roles in oxidative stress resistance and virulence. As a ferroxidase, Dps of Escherichia coli can protect bacteria from reactive oxygen species damage, but its role in bacterial pathogenesis has received little attention. In this study, FtpA of the swine respiratory pathogen A. pleuropneumoniae was identified as a new Dps-like protein. It facilitated A. pleuropneumoniae resistance to HO, survival in macrophages, and infection . FtpA could bind and oxidize Fe through two important residues in its ferroxidase site and protected the bacteria from oxidative damage mediated by the intracellular Fenton reaction. These findings provide new insights into the role of the FtpA-based antioxidant system in the pathogenesis of A. pleuropneumoniae, and the conserved Fe binding ligands in Dps/FtpA provide novel drug target candidates for disease prevention.