Lipotoxin F of Pseudomonas aeruginosa is an AlgU-dependent and alginate-independent outer membrane protein involved in resistance to oxidative stress and adhesion to A549 human lung epithelia

Chronic lung infection with P. aeruginosa and excessive neutrophil-associated inflammation are major causes of morbidity and mortality in patients with cystic fibrosis (CF). Overproduction of an exopolysaccharide known as alginate leads to the formation of mucoid biofilms that are resistant to antibiotics and host defences. Alginate overproduction or mucoidy is controlled by a stress-related ECF sigma factor AlgU/T. Mutation in the anti-sigma factor MucA is a known mechanism for conversion to mucoidy. Recently, we showed that inactivation of a kinase (KinB) in nonmucoid strain PAO1 results in overproduction of alginate. Here, we report the initial characterization of lipotoxin F (LptF, PA3692), an OmpA-like outer membrane protein that exhibited increased expression in the mucoid PAO1 kinB mutant. The lipotoxin family of proteins has been previously shown to induce inflammation in lung epithelia, which may play a role in CIF disease progression. Expression of LptF was observed to be AlgU-dependent and upregulated in CIF isolates. Deletion of IptF from the kinB mutant had no effect on alginate production. Deletion of IptF from PAO1 caused a differential susceptibility to oxidants that can be generated by phagocytes. The IptF and algU mutants were more sensitive to hypochlorite than PAO1. However, the IptF mutant displayed increased resistance to hydrogen peroxide. LptF also contributed to adhesion to A549 human lung epithelial cells. Our data suggest that LptF is an outer membrane protein that may be important for P. aeruginosa survival in harsh environments, including lung colonization in CF.