Oxidative responses and defense mechanism of hyperpigmented P. aeruginosa as characterized by proteomics and metabolomics

Pseudomonas aeruginosa is known to produce multiple types of pigment which are involved in its pathogenicity and survival in certain environments. Herein, we reported the identification of P. aeruginosa dark-brown hyperpigmented (HP) strains which have been isolated from clinical samples. In order to study the role of these dark-brown containing secretions, alterations of metabolic processes and cellular responses under microenvironment of this bacterial pathogen, two-dimensional gel electrophoresis (2-DE) in conjunction with peptide mass fingerprinting (PMF) were performed. Protein spots showing the most significant differences and high spot optical density values were selected for further characterization. Fold difference of protein expression levels among those spots were calculated. Three major groups of proteins including anti-oxidant enzyme such as catalase, alkyl hydroperoxide reductase and also iron-superoxide dismutase (Fe-SOD), transmembrane proteins as well as proteins involved in energy metabolism such as ATP synthase and pyruvate/2-oxoglutarate dehydrogenase were significantly decreased in P. aeruginosa HP. Whereas, malate syntase and isocitrate lyase, the key enzyme in glyoxylate cycle as well as alcohol dehydrogenase were significantly increased in P. aeruginosa HP, as compared to the reference strain ATCC 27853. Moreover, the HP exerted SOD-like activity with its IC(50) equal to 0.26 mg/ml as measured by NBT assay. Corresponding to secretomic metabolome identification, elevated amounts of anti-oxidant compounds are detected in P. aeruginosa HP than those observed in ATCC 27853. Our findings indicated successful use of proteomics and metabolomics for understanding cell responses and defense mechanisms of P. aeruginosa dark-brown hyperpigmented strains upon surviving in its microenvironment.