Pseudomonas aeruginosa Swarmer Cells Adaptation Toward UVc Radiations.

Swarming is the most rapid surface motility allowing Pseudomonas aeruginosa bacteria to rapidly colonize new surfaces. However, swarming behavior is affected by environmental factors like ultraviolet irradiation (UVc). UVc radiation is the most disinfection technology usually applied for wastewater and proven to be effective to inactivate microorganisms. However, efficiency against motile bacteria is not yet studied. This study aims to explain the mechanisms of resistance of swarmer P. aeruginosa cells toward UVc exposure. P. aeruginosa liquid cultures were allowed to swarm across a semisolid surface for 18 h and directly exposed to UVc radiations. Emergent swarmer colonies, revealed after re-incubation, were selected to study biofilm formation, fatty acid (FA) composition, and ultrastructure. Our results showed that membrane adaptation to UVc radiations was seen in Pseudomonas cells by an increase of cyclic fatty acid (CFA) content, confirming the role of cyclopropane in radio-resistance of swarmer cells. Furthermore, electron microscopic study confirmed that over production of S-layer is believed to be a protective form adopted by P. aeruginosa swarmer cells to resist after 5 min of UVc exposure. Moreover, membrane disintegration is the lethal effect observed after 15 min of UVc exposure. In the other hand, study of biofilm production showed an enhancement of biofilm formation, of swarmer cells mainly after 15 min of UVc exposure. There results confirmed that swarming process is highly correlated with particular FA composition of P. aeruginosa membrane and that radio-resistance of swarmer cells is highly supported by CFA biosynthesis and S-layer overproduction.

Antioxidant Defense Mechanisms in Pseudomonas aeruginosa: Role of Iron-Cofactored Superoxide Dismutase in Response to UV-C Radiations.

The role of SOD gene in response to UV-C radiations was studied in Pseudomonas aeruginosa. Firstly, our results showed that the inactivation of sodM and/or sodB genes decreases the resistance of P. aeruginosa after exposure to UV-C rays. Furthermore, our results showed that SOD activity is dose dependant in all strains. However, significant increase in SOD activity was only shown at UV-C exposure time of 5 min in sodB mutant. At an elevated dose equivalent to 30 min of exposure, significant increase in SOD activity was observed in sodM. Catalase activities showed significant decrease in WT and in sodB mutant after an exposure time of 30 min. CAT enzyme was present at higher levels than SOD, reflecting that alternate enzymes such as POX, is poorly associated with CAT activity, and an increase in POX activity is related to increase in stress tolerance. The overall results showed that sodB gene has an important protective role against UV-C radiations in P. aeruginosa, compared to SodM isoform.

Changes in membrane fatty acid composition of Pseudomonas aeruginosa in response to UV-C radiations.

The changes in lipid composition enable the micro-organisms to maintain membrane functions in the face of environmental fluctuations. The relationship between membrane fatty acid composition and UV-C stress was determined for mid-exponential phase and stationary phase Pseudomonas aeruginosa. The total lipids were obtained by dichloromethane/methanol (3:1) and were quantified by GC. The TLC analysis of phospholipids showed the presence of three major fractions phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Significant modifications, as manifested by an increase of UFA, were obtained. Interestingly, this microorganism showed a remarkable capacity for recovery from the stressful effects of UV-C.