PhoPQ two-component regulatory system plays a global regulatory role in antibiotic susceptibility, physiology, stress adaptation, and virulence in Stenotrophomonas maltophilia

Background: Stenotrophomonas maltophilia, an opportunistic pathogen, is ubiquitously present in various environments, signifying its high capability of environmental adaptation. Two-component regulatory system (TCS) is a powerful implement to help organisms to survive in different environments. In clinic, treatment of S. maltophilia infection is difficult because it is naturally resistant to many antibiotics, highlighting the necessity to develop novel drugs or adjuvants. Given their critical and extensively regulatory role, TCS system has been proposed as a convincing target for novel drugs or adjuvants. PhoPQ TCS, a highly conserved TCS in several pathogens, plays crucial roles in low-magnesium adaption, polymyxin resistance, and virulence. In this study, we aimed to characterize the role of PhoPQ TCS of S. maltophilia in antibiotic susceptibility, physiology, stress adaptation, and virulence. Results: To characterize PhoPQ system, phoP single mutant as well as phoP and phoQ double mutant were constructed. Distinct from most phoPQ systems of other microorganisms, two features were observed during the construction of phoP and phoQ single deletion mutant. Firstly, the phoQ mutant was not successfully obtained. Secondly, the compromised phenotypes of phoP mutant were not reverted by complementing an intact phoP gene, but were partially restored by complementing a phoPQ operon. Thus, wild-type KJ, phoP mutant (KJΔPhoP), phoPQ mutant (KJΔPhoPQ), and complemented strain (KJΔPhoPQ (pPhoPQ)) were used for functional assays, including antibiotic susceptibility, physiology (swimming motility and secreted protease activity), stress adaptation (oxidative, envelope, and iron-depletion stresses), and virulence to Caenorhabditis elegans. KJΔPhoPQ totally lost swimming motility, had enhanced secreted protease activity, increased susceptibility to antibiotics (β-lactam, quinolone, aminoglycoside, macrolide, chloramphenicol, and sulfamethoxazole/ trimethoprim), menadione, H₂O₂, SDS, and 2,2′-dipyridyl, as well as attenuated virulence to C. elegans. Trans-complementation of KJΔPhoPQ with phoPQ reverted these altered phenotypes to the wild-type levels. Conclusions: Given the critical and global roles of PhoPQ TCS in antibiotic susceptibility, physiology, stress adaptation, and virulence, PhoPQ is a potential target for the design of drugs or adjuvants.