Distinct roles of extracellular polymeric substances in Pseudomonas aeruginosa biofilm development

Abstract

Bacteria form surface attached biofilm communities as one of the most important survival strategies in nature. Biofilms consist of water, bacterial cells and a wide range of self-generated extracellular polymeric substances (EPS). Biofilm formation is a dynamic self-assembly process and several distinguishable stages are observed during bacterial biofilm development. Biofilm formation is shown to be coordinated by EPS production, cell migration, subpopulation differentiation and interactions. However, the ways these different factors affect each other and contribute to community structural differentiation remain largely unknown. The distinct roles of different EPS have been addressed in the present report. Both Pel and Psl polysaccharides are required for type IV pilus-independent microcolony formation in the initial stages of biofilm formation by Pseudomonas aeruginosa PAO1. Both Pel and Psl polysaccharides are also essential for subpopulation interactions and macrocolony formation in the later stages of P. aeruginosa PAO1 biofilm formation. Pel and Psl polysaccharides have different impacts on Pseudomonas quinolone signal-mediated extracellular DNA release in P. aeruginosa PAO1 biofilms. Psl polysaccharide is more important than Pel polysaccharide in P. aeruginosa PAO1 biofilm formation and antibiotic resistance. Our study thus suggests that different EPS materials play distinct roles during bacterial biofilm formation.

Genetic and phenotypic analysis of the GacS/GacA system in the moderate halophile Halomonas anticariensis

“…Importantly, biofilm formation was reduced in the H. anticariensis Gac mutants compared with the wild-type, which provides evidence that these two traits are correlated in this bacterium as they are in other micro-organisms. Lately, it has been reported that in Pseudomonas aeruginosa extracellular polymeric substances play a distinct key role during biofilm formation (Yang et al, 2011) and this development is controlled by TCSs among other elements such us QS, c-di-GMP and sigma factors (Mikkelsen et al, 2011). Since biofilm formation is a complex process controlled by multiple factors, the TCS might indirectly affect it by contributing to the regulation of some key genes, all of which requires further study.…”

Low concentrations of ethanol stimulate biofilm and pellicle formation in Pseudomonas aeruginosa

“…This result is consistent with previous reports that the biofilm-forming ability of PAO1 was attenuated in a mutant lacking Psl. 19,20) Low concentrations of ethanol repressed cell growth but stimulated biofilm formation in all strains except for the ΔpelAΔpslA mutant (Fig. 2(A)), suggesting that enhancement of biofilm formation by low concentrations of ethanol requires either Pel or Psl exopolysaccharide.…”

PslG, a self-produced glycosyl hydrolase, triggers biofilm disassembly by disrupting exopolysaccharide matrix

“…This exopolysaccharide also confers resistance of P. aeruginosa biofilms to antibiotics and phagocytic cells [9,[24][25][26]. In P. aeruginosa PAO1 (a common lab strain), Psl is more important than Pel for biofilm microcolony formation and antibiotic resistance [24]. In addition, Psl also plays an important role in the biofilm formation of mucoid strains [27], and can function as a signal to stimulate biofilm formation [28].…”

“…Psl, a repeating pentasaccharide containing D-mannose, D-glucose and L-rhamnose [23], acts as 'molecular glue' to promote bacterial cell-cell and cell-surface interactions and it can form a fiber-like web to enmesh bacterial communities [6,7,17]. This exopolysaccharide also confers resistance of P. aeruginosa biofilms to antibiotics and phagocytic cells [9,[24][25][26]. In P. aeruginosa PAO1 (a common lab strain), Psl is more important than Pel for biofilm microcolony formation and antibiotic resistance [24].…”