Recent data indicate that cystic fibrosis (CF) airway mucus is anaerobic. This suggests that Pseudomonas aeruginosa infection in CF reflects biofilm formation and persistence in an anaerobic environment. P. aeruginosa formed robust anaerobic biofilms, the viability of which requires rhl quorum sensing and nitric oxide (NO) reductase to modulate or prevent accumulation of toxic NO, a byproduct of anaerobic respiration. Proteomic analyses identified an outer membrane protein, OprF, that was upregulated approximately 40-fold under anaerobic versus aerobic conditions. Further, OprF exists in CF mucus, and CF patients raise antisera to OprF. An oprF mutant formed poor anaerobic biofilms, due, in part, to defects in anaerobic respiration. Thus, future investigations of CF pathogenesis and therapy should include a better understanding of anaerobic metabolism and biofilm development by P. aeruginosa.

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SummaryQuorum sensing (QS) governs the production of virulence factors and the architecture and sodium dodecyl sulphate (SDS) resistance of bio®lm-grown Pseudomonas aeruginosa. P. aeruginosa QS requires two transcriptional activator proteins known as LasR and RhlR and their cognate autoinducers PAI-1 (N-(3-oxododecanoyl)-L-homoserine lactone) and PAI-2 (Nbutyryl-L-homoserine lactone) respectively. This study provides evidence of QS control of genes essential for relieving oxidative stress. Mutants devoid of one or both autoinducers were more sensitive to hydrogen peroxide and phenazine methosulphate, and some PAI mutant strains also demonstrated decreased expression of two superoxide dismutases (SODs), Mn-SOD and Fe-SOD, and the major catalase, KatA. The expression of sodA (encoding Mn-SOD) was particularly dependent on PAI-1, whereas the in¯uence of autoinducers on Fe-SOD and KatA levels was also apparent but not to the degree observed with Mn-SOD. b-Galactosidase reporter fusion results were in agreement with these ®ndings. Also, the addition of both PAIs to suspensions of the PAI-1/2-de®cient double mutant partially restored KatA activity, while the addition of PAI-1 only was suf®cient for full restoration of Mn-SOD activity. In bio®lm studies, catalase activity in wild-type bacteria was signi®cantly reduced relative to planktonic bacteria; catalase activity in the PAI mutants was reduced even further and consistent with relative differences observed between each strain grown planktonically. While wild-type and mutant bio®lms contained less catalase activity, they were more resistant to hydrogen peroxide treatment than their respective planktonic counterparts. Also, while catalase was implicated as an important factor in bio®lm resistance to hydrogen peroxide insult, other unknown factors seemed potentially important, as PAI mutant bio®lm sensitivity appeared not to be incrementally correlated to catalase levels.