Two Genetic Loci Produce Distinct Carbohydrate-Rich Structural Components of thePseudomonas aeruginosaBiofilm Matrix

Abstract

Pseudomonas aeruginosa forms biofilms, which are cellular aggregates encased in an extracellular matrix. Molecular genetics studies of three common autoaggregative phenotypes, namely wrinkled colonies, pellicles, and solid-surface-associated biofilms, led to the identification of two loci, pel and psl, that are involved in the production of carbohydrate-rich components of the biofilm matrix. The pel gene cluster is involved in the production of a glucose-rich matrix material in P. aeruginosa strain PA14 (L. Friedman and R. Kolter, Mol. Microbiol. 51:675-690, 2004). Here we investigate the role of the pel gene cluster in P. aeruginosa strain ZK2870 and identify a second genetic locus, termed psl, involved in the production of a mannose-rich matrix material. The 11 predicted protein products of the psl genes are homologous to proteins involved in carbohydrate processing. P. aeruginosa is thus able to produce two distinct carbohydrate-rich matrix materials. Either carbohydrate-rich matrix component appears to be sufficient for mature biofilm formation, and at least one of them is required for mature biofilm formation in P. aeruginosa strains PA14 and ZK2870.Pseudomonas aeruginosa has been extensively utilized as a model organism for the study of biofilm formation (16,20). A key feature of mature P. aeruginosa biofilms is the presence of an extracellular matrix that encases the constituent cells. This matrix has been reported to contain a mixture of polymeric substances, including nucleic acids, proteins, and polysaccharides (11,(33)(34)(35). Matrix production occurs at a late stage in biofilm development, when cells display a high degree of autoaggregation (6, 27). The ability to autoaggregate leads to several macroscopic phenotypes; among them are the production of pellicles at the air-liquid interface of standing liquid cultures and the production of highly structured colonies on agar plates. Different strains of P. aeruginosa display variability in the abilities to form pellicles under different culture conditions and to show different colony morphologies. This phenotypic diversity most likely results from genetic differences among isolates (6, 11). Thus, we consider it important to perform genetic analyses of multiple strains.We recently identified the pel locus of P. aeruginosa strain PA14 (11). This locus contains seven genes whose products are required for matrix formation and which are therefore critical for the autoaggregative properties of the strain; pel mutants do not form pellicles or mature solid-surface-associated (SSA) biofilms. In addition, while the parent strain gives rise to wrinkled colonies under some growth conditions, the P. aeruginosa PA14 pel mutant colonies are invariably flat and smooth. The predicted protein products of the pel genes share sequence similarity with proteins involved in carbohydrate processing, and pel mutants lack a glucose-rich component of their extracellular matrix. Whether the pel genes are involved in the synthesis of a matrix component in other strains of P. aerugi...

Calcium-Induced Virulence Factors Associated with the Extracellular Matrix of MucoidPseudomonas aeruginosaBiofilms

“…Similar results were obtained using a mutant derivative of the nonmucoid strain P. aeruginosa PAO1 engineered to overproduce alginate (25,60). On the other hand, results using wild-type P. aeruginosa PAO1 and PA14 showed that alginate was not associated with biofilms (72) and that a second polysaccharide likely encoded by a separate polysaccharide biosynthetic gene cluster may provide the extracellular matrix material for those cells (18,19,29). In another report, using P. aeruginosa PAO1, DNA was suggested to be the extracellular matrix material, since the addition of DNase to biofilms dispersed the bacteria (64).…”

Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics

“…Psl was shown contributing to biofilm production, tolerance to oxidizing agents and host defensive processes (Friedman and Kolter, 2004;Jackson et al, 2004;Mishra et al, 2012), that is, traits likely useful in insect interactions.…”

High-Resolution Visualization ofPseudomonas aeruginosaPAO1 Biofilms by Freeze-Substitution Transmission Electron Microscopy

“…A recent study describing the EPS of PAO1 biofilms identified the major carbohydrate moieties in this to include glucose, rhamnose, mannose, xylose, 3-deoxy-D-manno-oct-2-ulosonic acid (KDO),N-acetylgalactosamine, N-acetylfucosamine, and N-acetylglucosamine (70). More recently, two genetic loci (psl and pel) responsible for the production of mannose-rich (psl) and glucose-rich (pel) polymer components of P. aeruginosa EPS (18,19,52) were identified. With the exception of KDO with its ionizable carboxylate, most of the sugars described in these studies are neutrally charged or sugars with a possible ionizable amine group (depending on polymeric linkage), which may be difficult to stain.…”