Abstract
Pseudomonas aeruginosa is an environmental bacterium and a nosocomial pathogen with clone C one of the most prevalent clonal groups. The P. aeruginosa clone C specific genomic island PACGI-1 harbors a xenolog of ftsH encoding a functionally diverse membrane-spanning ATP-dependent metalloprotease on the core genome. In the aquatic isolate P. aeruginosa SG17M, the core genome copy ftsH1 significantly affects growth and dominantly mediates a broad range of phenotypes, such as secretion of secondary metabolites, swimming and twitching motility and resistance to aminoglycosides, while the PACGI-1 xenolog ftsH2 backs up the phenotypes in the ftsH1 mutant background. The two proteins, with conserved motifs for disaggregase and protease activity present in FtsH1 and FtsH2, have the ability to form homo- and hetero-oligomers with ftsH2 distinctively expressed in the late stationary phase of growth. However, mainly FtsH1 degrades a major substrate, the heat shock transcription factor RpoH. Pull-down experiments with substrate trap-variants inactive in proteolytic activity indicate both FtsH1 and FtsH2 to interact with the inhibitory protein HflC, while the phenazine biosynthesis protein PhzC was identified as a substrate of FtsH1. In summary, as an exception in P. aeruginosa, clone C harbors two copies of the ftsH metallo-protease, which cumulatively are required for the expression of a diversity of phenotypes.
Highlights
Pseudomonas aeruginosa is a gram-negative opportunistic pathogen causing a broad spectrum of nosocomial infections in individuals with local or systemic immune system deficiency (Lyczak et al, 2000; Kerr and Snelling, 2009; Parkins et al, 2018)
The aquatic isolate SG17M is our reference clone C strain as it is the common assumption that environmental isolates infect patients (Römling et al, 1994; Martin et al, 2013)
Though, SG17M did not secrete effector proteins ExoS, ExoT, and ExoY of the type III secretion system (T3SS) under experimental conditions previously demonstrated to trigger type III secretion in P. aeruginosa (Toska et al, 2014; Figure S1B), despite that the invasive type SG17M codes for the T3SS locus and harbors the respective effector proteins
Summary
Pseudomonas aeruginosa is a gram-negative opportunistic pathogen causing a broad spectrum of nosocomial infections in individuals with local or systemic immune system deficiency (Lyczak et al, 2000; Kerr and Snelling, 2009; Parkins et al, 2018). FtsH functionality has been extensively characterized in Escherichia coli K-12 mainly with respect to protein degradation (Schumann, 1999; Bittner et al, 2017) In this strain, FtsH controls protein quality by degrading out-of-context (membrane) proteins such as the subunit alpha of the F1F0 ATP synthase complex and the type 2 secretion system translocon protein SecY and contributes to the decision between lysis and lysogeny upon bacteriophage λ infection (Ito and Akiyama, 2005). Besides its function as a protease of unstructured and misfolded proteins, FtsH together with HflC, HflK, and YIdC acts as a chaperone to maintain the integrity of inner membrane proteins (Van Bloois et al, 2008) In yet another functionality, FtsH aids the translocation of the cytotoxic C-terminal domain of the tRNAase toxin colicin D from the periplasm into the cytoplasm (Walker et al, 2007). The degradation of the heat shock sigma factor RpoH and processing of the phenazine biosynthesis protein PhzC are mainly FtsH1-dependent in P. aeruginosa SG17M
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