[S2-2] Cell surface alteration and increased membrane vesicle release in Pseudomonas aeruginosa biofilm
Many bacteria release membrane vesicles (MVs) ranging 20-400 nm from the bacterial surface into the extracellular milieu. We previously found that MV release is significantly increased at biofilm conditions as compared to planktonic conditions in an opportunistic pathogen Pseudomonas aeruginosa, but it has not been fully understood the mechanism of what factors induce MV formation in biofilms. Here, we investigated the alteration in surface conditions and factors involved in increased MV formation in P. aeruginosa biofilms. The quick-freeze deep etching and replica electron microscopy analysis revealed that the separation between outer and inner membranes was observed at biofilm, suggesting that biofilm-specific surface changes occur. There was no significant change in the protein composition of the outer membrane, but there was a notable difference in the phospholipid composition of the cell membrane between planktonic and biofilm states. Proteomic analyses revealed that proteins contained MVs are quite different between those conditions. Furthermore, we identified several factors, including exopolysaccharides, motilities and signals, related to MV induction. Thus, cell surface alteration and MV formation were induced by bioflm-specific extracellular substances in P. aeruginosa.