MrkD1Pfrom Klebsiella pneumoniae Strain IA565 Allows for Coexistence with Pseudomonas aeruginosa and Protection from Protease-Mediated Biofilm Detachment

Abstract

ABSTRACTBiofilm formation and persistence are essential components for the continued survival of pathogens inside the host and constitute a major contributor to the development of chronic wounds with resistance to antimicrobial compounds. Understanding these processes is crucial for control of biofilm-mediated disease. Though chronic wound infections are often polymicrobial in nature, much of the research on chronic wound-related microbes has focused on single-species models.Klebsiella pneumoniaeandPseudomonas aeruginosaare microbes that are often found together in wound isolates and are able to form stablein vitrobiofilms, despite the antagonistic nature ofP. aeruginosawith other organisms. Mutants of theK. pneumoniaestrain IA565 lacking the plasmid-bornemrkD1Pgene were less competitive than the wild type in anin vitrodual-species biofilm model withP. aeruginosa(PAO1). PAO1 spent medium inhibited the formation of biofilm ofmrkD1P-deficient mutants and disrupted preestablished biofilms, with no effect on IA565 and no effect on the growth of the wild type or mutants. A screen using a two-allele PAO1 transposon library identified the LasB elastase as the secreted effector involved in biofilm disruption, and a purified version of the protein produced results similar to those with PAO1 spent medium. Various other proteases had a similar effect, suggesting that the disruption of themrkD1Pgene causes sensitivity to general proteolytic effects and indicating a role for MrkD1Pin protection against host antibiofilm effectors. Our results suggest that MrkD1Pallows for competition ofK. pneumoniaewithP. aeruginosain a mixed-species biofilm and provides defense against microbial and host-derived proteases.