Abstract
Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. P. aeruginosa can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated P. aeruginosa strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. β-Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.
Highlights
Pseudomonas aeruginosa is a ubiquitous, Gram-negative bacterium that thrives in soil and aquatic environments, playing important roles in the carbon and nitrogen cycles
These results showed the shift of strain RBS population from swimming to swarming and the subsequent formation of microcolonies embedded in the biofilm matrix
The P. aeruginosa strain RBS was isolated from the saltern of Sfax in Tunisia
Summary
Pseudomonas aeruginosa is a ubiquitous, Gram-negative bacterium that thrives in soil and aquatic environments, playing important roles in the carbon and nitrogen cycles. During the last few decades, P. aeruginosa has become one of the most frequent causative agents of nosocomial infections in predisposed human subjects [2]. Because of its ability to grow and survive in various environmental conditions, P. aeruginosa infection becomes common and outbreaks of extreme drug-resistant strains are frequent among hospital wards and intensive care units [3]. In order to control and prevent these pseudomonal infections, understanding regulatory mechanisms governing virulence gene expression is crucial to develop alternative therapeutic interventions. P. aeruginosa produces a variety of virulence factors regulated by quorum sensing (QS): elastase (LasB), alkaline protease (AprA), protease A, exotoxin A, pyocyanin, and rhamnosyltransferase [4]. QS contributes to control the production of virulence factors, motility, motility-sessility switch, and biofilm development
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