Quorum sensing in Pseudomonas aeruginosa controls expression of catalase and superoxide dismutase genes and mediates biofilm susceptibility to hydrogen peroxide

Quorum sensing (QS) governs the production of virulence factors and the arc hitecture and sodium dodecyl sulphate (SDS) resistance of biofilm-grown Pse udomonas aeruginosa. P. aeruginosa QS requires two transcriptional activato r proteins known as LasR and RhIR and their cognate autoinducers PAI-1 (N-( 3-oxododecanoyl)-L-homoserine lactone) and PAI-2 (N-butyryl-L-homoserine la ctone) respectively. This study provides evidence of QS control of genes es sential for relieving oxidative stress. Mutants devoid of one or both autoi nducers were more sensitive to hydrogen peroxide and phenazine methosulphat e, and some PAI mutant strains also demonstrated decreased expression of tw o superoxide dismutases (SODs), Mn-SOD and Fe-SOD, and the major catalase, KatA. The expression of sodA (encoding Mn-SOD) was particularly dependent o n PAI-1, whereas the influence of autoinducers on Fe-SOD and KatA levels wa s also apparent but not to the degree observed with Mn-SOD. beta-Galactosid ase reporter fusion results were In agreement with these findings. Also, th e addition of both PAIs to suspensions of the PAI-1/2-deficient double muta nt partially restored KatA activity, while the addition of PAI-1 only was s ufficient for full restoration of Mn-SOD activity. In biofilm studies, cata lase activity in wild-type bacteria was significantly reduced relative to p lanktonic bacteria; catalase activity in the PAI mutants was reduced even f urther and consistent with relative differences observed between each strai n grown planktonically. While wild-type and mutant biofilms contained less catalase activity, they were more resistant to hydrogen peroxide treatment than their respective planktonic counterparts. Also, while catalase was imp licated as an important factor in biofilm resistance to hydrogen peroxide I nsult, other unknown factors seemed potentially important, as PAI mutant bi ofilm sensitivity appeared not to be incrementally correlated to catalase l evels.