Identification of type II and type III pyoverdine receptors from Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Bacterial Physiology
• Molecular Biology

Background:

• Pseudomonas aeruginosa utilizes pyoverdine (PVD) for iron uptake under iron-limited conditions.
• PVD interacts with outer membrane receptors, specifically TonB-dependent receptors like FpvA.
• Three PVD types (I-III) exist, but only the receptor for type I (FpvAI) was previously known.

Purpose of the Study:

• To identify and characterize the outer membrane receptors for type II and type III pyoverdine in Pseudomonas aeruginosa.
• To elucidate the genetic basis of PVD uptake and its role in bacterial growth and iron acquisition.

Main Methods:

• Mutagenesis of P. aeruginosa strains using mini-TnphoA3 transposon.
• Selection of mutants unable to grow with iron chelators and cognate PVD.
• Construction and screening of cosmid libraries for functional complementation.
• Determination of fpvA gene sequences for type II and type III PVD receptors.
• Allelic exchange mutagenesis and complementation studies.

Main Results:

• A mutant with a pvdE gene insertion was unable to uptake type II PVD and resistant to pyocin S3.
• A second mutant with an fpvA insertion was unable to uptake type III PVD.
• Complementation studies identified functional type II and type III fpvA genes.
• Both type II and type III fpvA restored PVD uptake, growth, and iron acquisition.
• Type II fpvA also restored sensitivity to pyocin S3.

Conclusions:

• The FpvA receptor is essential for the uptake of cognate PVD types in P. aeruginosa.
• Novel type II and type III FpvA receptors have been identified and characterized.
• These findings expand the understanding of siderophore-mediated iron transport in P. aeruginosa.
• Structural similarities and differences in FpvA receptors, including N-terminal extensions, were noted.