Cell Surface Hydrophobicity as a Pellicle Formation Factor in Film Strain of Saccharomyces

In nature, Saccharomyces yeasts manifest a number of adaptive responses to overcome adverse environments such as filamentation, invasive growth, flocculation and adherence to solid surfaces. Certain Saccharomyces wild yeasts, namely ''flor yeasts,'' have also acquired the ability to form a buoyant biofilm at the broth surface. Here we report that mutations in a single gene, identified as FLO11, separate these ''floating'' yeasts from their nonfloating relatives. We have determined that the capability to form a self-supporting biofilm at the liquid surface is largely dependent on two changes in the FLO11 gene. First, we identified a 111-nt deletion within a repression region of the FLO11 promoter that significantly increases FLO11 gene expression. Secondly, we found rearrangements within the central tandem repeat domain of the coding region that yield a more hydrophobic Flo11p variant. Together, these mutations result in dramatic increase in cell surface hydrophobicity, which in turn confers these yeasts the ability to float by surface tension, an adaptive mechanism to gain direct access to oxygen within oxygen-poor liquid environments.adaptive mechanism ͉ buoyant biofilm ͉ yeast hydrophobicity

Proc. Natl. Acad. Sci. U.S.A.

“…It has been reported that flor yeasts possess high levels of surface hydrophobicity (40). In laboratory strains, it has been shown that hydrophobicity is largely dependent on FLO11 (17).…”

Section: Variations In the Flo11pmentioning

confidence: 99%

Adaptive evolution by mutations in theFLO11gene

Fidalgo

Barrales

Ibeas

et al. 2006

185

209

“…In contrast to other microbial biofilms, those formed by flor strains appear to consist of a layer of buoyant cells without a suspending extracellular polysaccharide or protein matrix, as no evidence for such extracellular material has been reported. Biofilm cells have been found to have an elevated and/or altered lipid content and an increased surface hydrophobicity (7,9,15,16,24). Recently, Zara et al (35) found that the small heat shock protein Hsp12 is required for biofilm formation in a Sardinian flor strain.…”

mentioning

confidence: 99%

FLO11-Based Model for Air-Liquid Interfacial Biofilm Formation bySaccharomyces cerevisiae

Bakalinsky

et al. 2005

Appl Environ Microbiol

106

109

Sardinian wine strains of Saccharomyces cerevisiae used to make sherry-like wines form a biofilm at the air-liquid interface at the end of ethanolic fermentation, when grape sugar is depleted and further growth becomes dependent on access to oxygen. Here, we show that FLO11, which encodes a hydrophobic cell wall glycoprotein, is required for the air-liquid interfacial biofilm and that biofilm cells have a buoyant density greater than the suspending medium. We propose a model for biofilm formation based on an increase in cell surface hydrophobicity occurring at the diauxic shift. This increase leads to formation of multicellular aggregates that effectively entrap carbon dioxide, providing buoyancy. A visible biofilm appears when a sufficient number of hydrophobic cell aggregates are carried to and grow on the liquid surface.Flor or velum formation by certain wine strains of Saccharomyces cerevisiae (flor strains) is a form of cellular aggregation that manifests as an air-liquid interfacial biofilm at the end of alcoholic fermentation. Increased cell buoyancy and the resultant biofilm that forms on the wine surface appear to be an adaptive mechanism because the biofilm assures access to oxygen and therefore permits continued growth on nonfermentable ethanol. In general, nonbuoyant cells cease growth at the end of completed wine fermentations not for lack of carbon, but for lack of oxygen. In contrast to other microbial biofilms, those formed by flor strains appear to consist of a layer of buoyant cells without a suspending extracellular polysaccharide or protein matrix, as no evidence for such extracellular material has been reported. Biofilm cells have been found to have an elevated and/or altered lipid content and an increased surface hydrophobicity (7,9,15,16,24). Recently, Zara et al. (35) found that the small heat shock protein Hsp12 is required for biofilm formation in a Sardinian flor strain. Reynolds and Fink (28) reported that a laboratory strain of S. cerevisiae could be induced to form a biofilm at a liquid-hydrophobic solid interface and that such formation was dependent on FLO11. In addition, flo11⌬ mutants were reported to be less hydrophobic than the wild type.FLO11 has an open reading frame (ORF) of 4,104 bp, which encodes a hydrolase belonging to the glycosylphosphatidylinositol-anchored class of cell wall proteins rich in serine and threonine. The central domain of Flo11 is similar to that of the flocculins Flo1, Flo5, and Flo10 (33). The FLO11 promoter is at least 2,800 bp (22) and is complex, consisting of four upstream activating sequences and at least nine upstream repressing sequences, the activities of which depend upon growth stage and nutritional conditions (30). In the present study, we demonstrate that FLO11 is required for yeast biofilm formation at an air-liquid interface and that the biofilm cells are not less dense than the suspending medium, and we propose a model to explain the role of FLO11 in biofilm formation. MATERIALS AND METHODSYeast strains, media, and genetic methods. ...

“…In general, nonbuoyant cells cease growth at the end of completed wine fermentations not for lack of carbon but for lack of oxygen. Biofilm cells have been found to have an elevated and/or altered lipid content and increased surface hydrophobicity (3,5,8,9,11). While both Hsp12, a small heat shock protein (13), and Muc1 (also known as Flo11), a hydrophobic cell wall mannoprotein (4, 6), have been shown to be required for the flor biofilm (10,12,14), other genetic or environmental requirements, other than an absence of glucose and the presence of ethanol and oxygen, have not been demonstrated.…”

mentioning

confidence: 99%

Ethanol-Independent Biofilm Formation by a Flor Wine Yeast Strain ofSaccharomyces cerevisiae

Groß

et al. 2010

Appl Environ Microbiol

Flor strains of Saccharomyces cerevisiae form a biofilm on the surface of wine at the end of fermentation, when sugar is depleted and growth on ethanol becomes dependent on oxygen. Here, we report greater biofilm formation on glycerol and ethyl acetate and inconsistent formation on succinic, lactic, and acetic acids.Flor or velum formation by certain wine strains of Saccharomyces cerevisiae (flor strains) is a form of cellular aggregation observed as an air-liquid interfacial biofilm at the end of the alcoholic fermentation. Formation of the biofilm appears to be an adaptive mechanism because it ensures access to oxygen and therefore permits continued growth on nonfermentable ethanol. In general, nonbuoyant cells cease growth at the end of completed wine fermentations not for lack of carbon but for lack of oxygen. Biofilm cells have been found to have an elevated and/or altered lipid content and increased surface hydrophobicity (3,5,8,9,11). While both Hsp12, a small heat shock protein (13), and Muc1 (also known as Flo11), a hydrophobic cell wall mannoprotein (4, 6), have been shown to be required for the flor biofilm (10,12,14), other genetic or environmental requirements, other than an absence of glucose and the presence of ethanol and oxygen, have not been demonstrated. Here, we asked whether flor formation could be induced during growth on nonfermentable substrates other than ethanol. On the basis of dry weight of biofilm formed per mg of available carbon, the best carbon sources were found to be glycerol, ethyl acetate, and ethanol, in descending order. While subsurface growth occurred on acetic, DL-lactic, and succinic acids, an air-liquid interfacial biofilm did not always form. Microarray analysis of cells shifted from growth on glucose to growth on ethanol did not detect significant changes in expression of known biofilm formation-associated genes.Yeast strain, growth conditions, and quantitation of biofilm. A flor strain of S. cerevisiae, 3238-32 MATa leu2-⌬1 lys2-801 ura3-52 (12), was grown for 24 h in YEPD (2% Bacto peptone, 1% yeast extract, 2% glucose) at 30°C and 200 rpm. Cells were harvested and washed twice in sterile distilled water by centrifugation, resuspended in sterile distilled water, and diluted 500-fold into sterile-filtered YNB (Bacto yeast nitrogen base without amino acids) plus 30 g/ml Leu, 30 g/ml Lys, and 10 g/ml Ura and supplemented with 4% (vol/vol) ethanol (YNBEtOH), 3% (vol/vol) glycerol (YNB-Glyc), 1% (wt/vol) potassium acetate (YNB-Acet), 2% (wt/vol) DL-lactic acid (YNBLact), 2% (wt/vol) succinic acid (YNB-Succ), or 2% (vol/vol) ethyl acetate (YNB-EtAc). All YNB-based media were adjusted to pH 5.4. Four replicate 1-ml/well cultures were grown in a 24-well polystyrene microtiter plate (Becton Dickinson Labware, NJ). Biofilms were harvested by aspiration after 5 days of static incubation at 30°C by collecting the 1-ml cultures and an additional 1 ml of sterile distilled water used to rinse each well. The 2-ml samples were transferred to a cuvette and read at A 600 . Biofilm bio...