The formation of biofilms and flocs is thought to be regulated by similar genes. There is also evidence that flocs contain an extracellular matrix, a biofilm-related trait, reflecting the close relationship between biofilm and floc phenotypes ( Beauvais et al. Flocculent clumps have been shown to render the participating yeast cells more resistant to chemical stresses ( Smukalla et al. Due to the intercellular bonds, flocculation is different from the type of clumping that results from motherвЂ“daughter cell separation defects. This phenotype is most commonly observed as clumping and settling in liquid media ( Johnston and Reader 1983 Liu et al. Flocs, in contrast to true biofilms, are clumps of yeast adhering to each other by a proteinвЂ“carbohydrate bond between cell surface proteins and cell wall sugars ( Bony et al. 2000 Reynolds and Fink 2001 Granek and Magwene 2010 Stovicek et al. Biofilms can be observed phenotypically by several assays including examination of a strainвЂ™s ability to adhere to polystyrene surfaces, visualized by staining, a strainвЂ™s ability to form a complex colony with an extracellular matrix, and its ability to form a complex mat on low agar media ( OвЂ™Toole and Kolter 1998 OвЂ™Toole et al.

The matrix is made up of secreted proteins and the biofilm is anchored to surfaces by hydrophobic interactions between yeast cell surface proteins and the surface ( Voordeckers et al. A true biofilm requires that yeast both form an extracellular protein matrix and adhere to a surface ( Stovicek et al. Yeast flocs and biofilms are two distinct but related phenotypes regulated by environmental changes that cause complex signaling and gene expression responses. As a result, biofilm formation has been selected against in most laboratory strains and our knowledge of the genetic basis of yeast biofilm formation remains incomplete. In the laboratory, yeast biofilms create significant challenges for many experiments. In brewing, yeast flocs facilitate easy removal of yeast from the final product, but yeast biofilms can complicate biofuel production and help pathogenic yeast remain virulent on hospital surfaces and during infection ( Verstrepen et al. The ability of yeast to form biofilms contributes to better survival under stress and affects myriad processes important to human health and industry. Wild-type budding yeast selectively bind to each other and to substrates in cohesive groups called yeast вЂњflocsвЂќ (or clumps) and yeast biofilms. This is a more complex view of the impact of ploidy on biofilm-related phenotypes than previous work with laboratory strains has suggested, demonstrating the importance and enormous potential of working with natural isolates of yeast. We also show that the phenotypic strength of these strains varies significantly depending on ploidy, and the diploid strains demonstrate both decreased and increased phenotypic strength with respect to their haploid counterparts. Our results show that there is extensive phenotypic variation between and within strains, and that these six phenotypes are primarily uncorrelated or weakly correlated, with the notable exception of complex colony and complex mat formation. We present a panel of 31 haploid and 24 diploid strains for which we have characterized six biofilm-related phenotypes: complex colony morphology, complex mat formation, flocculation, agar invasion, polystyrene adhesion, and psuedohyphal growth. A new collection of sequenced natural isolates from the Saccharomyces Genome Resequencing Project enabled us to examine the breadth of biofilm-related phenotypes in geographically, ecologically, and genetically diverse strains of Saccharomyces cerevisiae. Despite the importance of biofilms in yeast natural isolates, the majority of our knowledge about yeast biofilm genetics comes from work with a few tractable laboratory strains.

We see the impact of yeast biofilms and вЂњflocsвЂќ (clumps) in human health and industry, where forming clumps enables yeast to act as a natural filter in brewing and forming biofilms enables yeast to remain virulent in cases of fungal infection. The ability of yeast to form biofilms contributes to better survival under stressful conditions.

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