Fungal Super Glue: The Biofilm Matrix and Its Composition, Assembly, and Functions

Biofilms are arguably the most common state of microbial growth found in nature and in patients infected with pathogenic organisms. A canonical feature of prokaryotic and eukaryotic biofilms is their production of an extracellular matrix (Fig 1). The matrix provides a protective environment for biofilm cells, offering a three-dimensional framework for both surface adhesion and cell cohesion [1,2]. In addition, this extracellular material controls cell dispersion from the biofilm and provides a nutrient source for the community [3]. The physical barrier formed by the matrix is also clinically relevant, as it shields cells from environmental threats, including immune cells and antimicrobial drugs used for treatment [4,5]. This defensive characteristic has been demonstrated for biofilms formed by diverse fungal pathogens, including Aspergillus, Candida, Cryptococcus, and Saccharomyces, with Aspergillus fumigatus and Candida albicans being the best studied [2,5–8]. Biofilm-associated Candida infections are the fourth cause for nosocomial infections (predominantly infecting medical devices), which may lead to systemic infection associated with high mortality rates. Candida spp. are also the most common cause of mucosal infection of the oral and vaginal sites, where biofilm infection has been increasingly recognized. Despite the ubiquitous nature of the biofilm matrix, we are only beginning to understand the synthesis and composition of this material for a handful of species. This review will discuss select components of the extracellular matrix of fungal biofilms, including their synthesis, structure, and function.