Protein profiling analyses of the outer membrane of Burkholderia cenocepacia reveal a niche-specific proteome.

Outer membrane proteins (OMPs) are integral β-barrel proteins of the Gram-negative bacterial cell wall and are crucial to bacterial survival within the macrophages and for eukaryotic cell invasion. Here, we used liquid chromatography tandem mass spectrometry (LC-MS/MS) to comprehensively assess the outer membrane proteome of Burkholderia cenocepacia, an opportunistic pathogen causing cystic fibrosis (CF), in conditions mimicking four major ecological niches: water, CF sputum, soil, and plant leaf. Bacterial cells were harvested at late log phase, and OMPs were extracted following the separation of soluble proteins by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D-SDS-PAGE). Protein bands were excised and identified by LC-MS/MS analysis. The proteins identified under various growth conditions were further subjected to in silico analysis of gene ontology (subcellular localization, structural, and functional analyses). Overall, 72 proteins were identified as common to the four culture conditions, while 33, 37, 20, and 10 proteins were exclusively identified in the water, CF sputum, soil, and plant leaf environments, respectively. The functional profiles of the majority of these proteins revealed significant diversity in protein expression between the four environments studied and may indicate that the protein expression profiles are unique for every condition. Comparison of OMPs from one strain in four distinct ecological niches allowed the elucidation of proteins that are essential for survival in each niche, while the commonly expressed OMPs, such as RND efflux system protein, TonB-dependent siderophore receptor, and ABC transporter-like protein, represent promising targets for drug or vaccine development.