The Distribution of Multiple Exopolysaccharides in Pseudomonas syringae Biofilms

Abstract

Exopolysaccharides play important roles in 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 the impact of the exopolysaccharides, levan and alginate, on biofilm formation, we compared biofilms of Pseudomonas syringae PG4180 strains with different exopolysaccharide patterns. The mucoid strain PG4180 (PG4180.muc), which produced levan and alginate, and its levan-and/or alginate-deficient derivatives all formed biofilms in the wells of microtitre plates and in flow-chambers. We applied confocal laser scanning microscopy (CLSM) with fluorescently labelled lectins to investigate the spatial distribution of levan and an additional yet-unknown exopolysaccharide in flow chamber biofilms. The lectin Concanavalin A (ConA) bound specifically to levan and accumulated in cell-depleted voids in the centers 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. Production of a yet-to-be characterized additional exopolysaccharide might be more important for biofilm formation than the syntheses of levan and alginate.

Bacterial exopolysaccharides: biosynthesis pathways and engineering strategies

“…This phenomenon of the genetic equipment for the production of more than one EPS is also very widespread amongst microbes ( Christensen et al, 1985 ; Sutherland, 2001 ; Wozniak et al, 2003b ; Laue et al, 2008 ) and complicates the defined analysis of sugar moieties making up the polymer ( Rühmann et al, 2015 ).…”

Genome-Based Taxonomy of Species in the Pseudomonas syringae and Pseudomonas lutea Phylogenetic Groups and Proposal of Pseudomonas maioricensis sp. nov., Isolated from Agricultural Soil

“…Pseudomonas species are ubiquitous, but some are preferentially present in the environment, including soil ( Pseudomonas putida group) or fresh water ( Pseudomonas fluorescens group); others are known to be pathogenic to humans ( Pseudomonas aeruginosa group) or insects ( Pseudomonas entomophila ), and finally, some are related to plants, including those that are beneficial ( Pseudomonas protegens group) and those that are pathogens ( Pseudomonas syringae group) [ 2 ]. Pseudomonads can cause diseases in an array of plant species [ 3 , 4 , 5 ], and P. syringae is considered the top species within the top 10 plant pathogenic bacteria [ 6 ]; however, its taxonomy is controversial, and many strains are included in the so-called P. syringae species complex, which is phenotypically divided into more than 60 pathovars that can cause diseases in monocots, dicots and woody plants [ 7 ]. Pathovars are not always supported by phylogenetic traits, but at least a total of thirteen phylogenetic groups have been devised based on the similarity of housekeeping genes [ 8 ].…”