Mucoid Coating Provides a Growth Advantage to Pseudomonas aeruginosa at Oil–Water Interfaces

Chronic lung infection with bacterial biofilms is one of the leading causes of death in cystic fibrosis (CF) patients. Among many species infecting the lung airways, Pseudomonas aeruginosa is the major pathogen colonizing and persisting throughout the patient's life. The microorganism undergoes pathoadaptation, while switching from a nonmucoid to a mucoid phenotype, improving the mechanical properties of the resulting biofilms. Previous investigation of the dynamic rheological properties of nonmucoid (PANT) and mucoid (PASL) clinical P. aeruginosa isolates exposed to interfacial stresses demonstrated that the mucoid strains formed films with stronger resistance to bending and nonlinear relaxation to compression and tension. We hypothesize that the mucoid switch provides a growth advantage to P. aeruginosa through the development of interfacial films with viscoelastic properties enabling cell survival. Here, we investigate the physiological response of the mucoid and the nonmucoid P. aeruginosa to interfacial entrapment. Our results, both macroscopic and molecular, reveal that mucoid coating plays an important role in protecting the bacteria from interfacial stresses. Cell characterizations using electron and fluorescence microscopies showed higher proportion of dead nonmucoid cells compared to mucoid cells on interfacial exposure. For example, scanning transmission electron microscopy (STEM) imaging showed that 96.6% of nonmucoid cells vs only 22.2% of mucoid cells were lysed owing to interfacial stress. Furthermore, the transcriptional profiling of P. aeruginosa cells indicated the upregulation of pel, psl, and alginate genes encoding for exopolysaccharide biomaterials is associated with mucoid cells' ability to cope with the interfacial environments. Further characterization of real-time gene regulation at interfaces will elucidate the effects of interfacial environment on the regulation of bacterial virulence.