Contribution of alginate and levan production to biofilm formation by Pseudomonas syringae

Abstract

Exopolysaccharides (EPSs) play important roles in the attachment of bacterial cells to a surface and/or in building and maintaining the three-dimensional, complex structure of bacterial biofilms. To elucidate the spatial distribution and function of the EPSs levan and alginate during biofilm formation, biofilms of Pseudomonas syringae strains with different EPS patterns were compared. The mucoid strain PG4180.muc, which produces levan and alginate, and its levan-and/or alginate-deficient derivatives all formed biofilms in the wells of microtitre plates and in flow chambers. Confocal laser scanning microscopy with fluorescently labelled lectins was applied to investigate the spatial distribution of levan and an additional as yet unknown EPS in flow-chamber biofilms. Concanavalin A (ConA) bound specifically to levan and accumulated in cell-depleted voids in the centres of microcolonies and in blebs. No binding of ConA was observed in biofilms of the levan-deficient mutants or in wild-type biofilms grown in the absence of sucrose as confirmed by an enzyme-linked lectin-sorbent assay using peroxidase-linked ConA. Time-course studies revealed that expression of the levan-forming enzyme, levansucrase, occurred mainly during early exponential growth of both planktonic and sessile cells. Thus, accumulation of levan in biofilm voids hints to a function as a nutrient storage source for later stages of biofilm development. The presence of a third EPS besides levan and alginate was indicated by binding of the lectin from Naja mossambica to a fibrous structure in biofilms of all P. syringae derivatives. Production of the as yet uncharacterized additional EPS might be more important for biofilm formation than the syntheses of levan and alginate.

Appendage-Mediated Surface Adherence of Sulfolobus solfataricus

“…Since we detected glucose and galactosyl residues by lectin staining, lactose might be present as a breakdown product of the EPS. Studies on bacterial EPS in biofilm suggest that glycosylation functions as a means for nutrition storage (4,6,9,11,18). Therefore, it will be interesting to determine the purpose of EPS in archaea and whether it is composed only of sugars or contains proteins besides the flagellins and pilins.…”

The EPS Matrix: The “House of Biofilm Cells”

“…Overproduction of the Psl polysaccharide led to enhanced cell surface and intercellular adhesion of P. aeruginosa, which translated into significant changes in the architecture of the biofilm (14). Nevertheless, other polysaccharides produced by Pseudomonas spp., such as levan, may have a role in biofilm formation (13). P. aeruginosa has been widely used by many biofilm researchers; it is, metaphorically speaking, the Escherichia coli of biofilm research.…”

Sensor Kinases RetS and LadS RegulatePseudomonas syringaeType VI Secretion and Virulence Factors

“…syringae B728a utilizes protein secretion systems, exopolysaccharides, and other virulence factors during its interactions with its host. P. syringae is known to produce at least two EPSs: the polyfructan levan and the capsular polysaccharide alginate (44). Levan is a highmolecular-weight ␤-(2,6)-polyfructan that is thought to function as an extracellular storage compound metabolized by P. syringae during periods of nutrient deprivation (44).…”