Community participation in biofilm matrix assembly and function

Abstract

Biofilms of the fungus Candida albicans produce extracellular matrix that confers such properties as adherence and drug resistance. Our prior studies indicate that the matrix is complex, with major polysaccharide constituents being α-mannan, β-1,6 glucan, and β-1,3 glucan. Here we implement genetic, biochemical, and pharmacological approaches to unravel the contributions of these three constituents to matrix structure and function. Interference with synthesis or export of any one polysaccharide constituent altered matrix concentrations of each of the other polysaccharides. Each of these was also required for matrix function, as assessed by assays for sequestration of the antifungal drug fluconazole. These results indicate that matrix biogenesis entails coordinated delivery of the individual matrix polysaccharides. To understand whether coordination occurs at the cellular level or the community level, we asked whether matrix-defective mutant strains could be coaxed to produce functional matrix through biofilm coculture. We observed that mixed biofilms inoculated with mutants containing a disruption in each polysaccharide pathway had restored mature matrix structure, composition, and biofilm drug resistance. Our results argue that functional matrix biogenesis is coordinated extracellularly and thus reflects the cooperative actions of the biofilm community.biofilm | matrix | Candida | polysaccharide | resistance

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

“…Exopolysaccharides are a common component of the extracellular matrix in biofilms formed by many Gram-positive, Gram-negative bacteria and fungus C. albicans [6,[40][41][42]. In this study, we report that PslG, a glycoside hydrolase, prevents the biofilm formation of Pseudomonas species and efficiently disrupts their existing biofilms at nanomolar concentrations.…”

Fluconazole impacts the extracellular matrix of fluconazole-susceptible and -resistant Candida albicans and Candida glabrata biofilms

“…Candida biofilm matrix has α-1,2 branched and α-1,6 mannans (WSPs) associated with β-1,6 glucans (ASPs), constituting a mannan–glucan complex (MGCx) [26]. Considering that interactions of ECM polysaccharides are required for biofilm antifungal resistance [52], the reduction on WSP amounts in the ECM of the biofilms in the presence of FLZ might alter the constitution of the MGCx, leading to a higher susceptibility of the biofilms to antifungal therapy. Another notable finding of this study was that FLZ caused an important antibiofilm activity by causing a significant reduction in the total biomasses of all the yeasts studied.…”

“…The ASPs, such as β-1,3 glucans, sequestrate antifungals preventing them from diffusing through the ECMs of C. albicans [22,52–55] and non- albicans biofilms [56]. It has been demonstrated that β-1,3 glucan has a role in antifungal resistance as it binds to FLZ avoiding this drug to reach its targets [22,52–56]. Thus, ASP’s significant reduction in the ECM of CaS biofilms demonstrates that the biofilms of this specific strain become more vulnerable when FLZ is present.…”

Biofilm Exopolysaccharides of Pathogenic Fungi: Lessons from Bacteria

“…albicans, the most common fungal pathogen of humans, forms extensive biofilms on medical devices and mucosal surfaces during infection (1,2). Studies of the biofilm matrix have revealed a cooperative role of ␤-1,3-glucans with a mannanglucan complex in the development and maintenance of biofilm structure (3,4). Although similar polysaccharides are also found within the fungal cell wall, the synthesis of the matrix polysaccharides is governed by pathways independent of those that mediate cell wall synthesis.…”

“…␤-1,3-Glucans within the C. albicans biofilm matrix play an important role in sequestration of antifungal agents (5) and in masking fungal cells from recognition by neutrophils (6). In contrast, biofilms formed by the mold A. fumigatus have been reported during pulmonary infection (7) and are dependent on the exopolysaccharide galactosaminogalactan (GAG) 3 (8). GAG is a partially deacetylated heteropolymer of ␣-1,4-linked galactose and N-acetyl galactosamine, which mediates adhesion between both fungi and also to other surfaces as well as protection against host immune defenses (8 -11).…”