Novel Entries in a Fungal Biofilm Matrix Encyclopedia

Abstract

Virulence of Candida is linked with its ability to form biofilms. Once established, biofilm infections are nearly impossible to eradicate. Biofilm cells live immersed in a self-produced matrix, a blend of extracellular biopolymers, many of which are uncharacterized. In this study, we provide a comprehensive analysis of the matrix manufactured by Candida albicans both in vitro and in a clinical niche animal model. We further explore the function of matrix components, including the impact on drug resistance. We uncovered components from each of the macromolecular classes (55% protein, 25% carbohydrate, 15% lipid, and 5% nucleic acid) in the C. albicans biofilm matrix. Three individual polysaccharides were identified and were suggested to interact physically. Surprisingly, a previously identified polysaccharide of functional importance, β-1,3-glucan, comprised only a small portion of the total matrix carbohydrate. Newly described, more abundant polysaccharides included α-1,2 branched α-1,6-mannans (87%) associated with unbranched β-1,6-glucans (13%) in an apparent mannan-glucan complex (MGCx). Functional matrix proteomic analysis revealed 458 distinct activities. The matrix lipids consisted of neutral glycerolipids (89.1%), polar glycerolipids (10.4%), and sphingolipids (0.5%). Examination of matrix nucleic acid identified DNA, primarily noncoding sequences. Several of the in vitro matrix components, including proteins and each of the polysaccharides, were also present in the matrix of a clinically relevant in vivo biofilm. Nuclear magnetic resonance (NMR) analysis demonstrated interaction of aggregate matrix with the antifungal fluconazole, consistent with a role in drug impedance and contribution of multiple matrix components.

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

“…This result corroborates to a previous finding that observed that a strain defective in hyphae formation (Δ/Δ efg1) was capable of producing eDNA similar to its parental strains that formed hyphae [35]. In C. albicans , eDNA contributes to the preservation and stability of mature biofilms, but not to their establishment [24,25], while the recognized role of some proteins is linked to metabolism [26]. In addition, eDNA performs as a regulator of biofilm cell antifungal resistance against echinocandins and amphotericin B but does not seem to significantly contribute to FLZ resistance [59].…”

“…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.…”

“…In addition to β-glucan, it has been reported that extracellular DNA (eDNA) is also an important ECM constituent and one that promotes structural integrity of candidal biofilms [25]. Furthermore, nuclear magnetic resonance investigation verified interaction of ECM with FLZ, demonstrating a role in drug resistance [26]. …”

Streptococcus gordonii comCDE (competence) operon modulates biofilm formation with Candida albicans

“…Incubation of the biofilms with lyticase led to~50 % reduced biomass, suggesting the presence of b-glucans, which are derived from C. albicans cell wall turnover (Xie et al, 2012). The EPS of C. albicans biofilms comprises .50 % protein, branched-chain mannans, mannan-glucan complexes and a small proportion (~5 %) of eDNA (Zarnowski et al, 2014). The EPS of C. albicans biofilms is known to contribute to antifungal drug resistance (Taff et al, 2013).…”

“…C. albicans biofilms contain~50 % protein, as well as mannan, glucan and eDNA (Zarnowski et al, 2014). Incubation of monospecies biofilms of S. gordonii with DNase I, proteinase K or lyticase (b-1,3-glucan hydrolase) resulted in small but not statistically significant effects on biomass (Fig.…”