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Lab of Industrial Microbiology, Korea university 2010010566 Hyeon Jeong Eun

Lab of Industrial Microbiology, Korea university 2010010566 Hyeon Jeong Eun. Introduction. Adhesion & Flocculation. One of the most critical functions of the cell surface Prevents cells from being washed away Allows them to form biofilms that offer protection ability.

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Lab of Industrial Microbiology, Korea university 2010010566 Hyeon Jeong Eun

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  1. Lab of Industrial Microbiology, Korea university 2010010566 HyeonJeongEun

  2. Introduction • Adhesion & Flocculation • One of the most critical functions of the cell surface • Prevents cells from being washed away • Allows them to form biofilms that offer protection ability • Fungal (Yeast) Adhesion • 1) Adhere to abiotic surfaces such as plastic • 2) Cell-Cell adhesion ( Flocculation ) • =>Phenotypic variability and plasticity

  3. Introduction • Biofilm • A complex aggregation of microorganisms marked by the excretion of a protective and adhesive matrix • J. Valle et al., “Broad-spectrum biofilm inhibition by a secreted bacterial polysaccharide,” PNAS 103(33): 12558-12563. 2006. • Medical and industrial relevance of fungal adhesion • 1) The remarkable plasticity -> New drugs • 2) Separate biomass from various fermentation products

  4. Adhesins or Flocculins ; Specialized cell-surface proteins • Bind specific amino acid or sugar residues • A common three-domain structure • 1) C-terminal : Glycosylphosphatidylinositol (GPI)-anchor 2) N-terminal : Carbohydrate or peptide binding domain • 3) Middle domain : Multiple serine and threonine-rich repeats

  5. Fig1. Secretion and cell-surface anchoring of fungal adhesins

  6. FigS1. Phylogenetic tree of cellular adhesins and mucins

  7. Fig2. Cell-cell and cell-surface adhesion associated with the S. cerevisiae FLO genes [1] Expresses the FLO1 [2] Does not express any FLO gene [3] Overexpresses FLO11

  8. Different of mechanisms of adhesion • 1) Lectin-like adhesion (sugar sensitive) • N-terminus : lectin-like carbohydrate binding domain • Two sub-categories - Flo1 group : only binds mannose sugars - NewFlo group : binds various sugars • 2) Sugar-insensitive adhesion • bind peptides or increase the cell-surface hydrophobicity

  9. Controlled by several signaling pathways • Triggered by certain stress factors and/or nutrient limitation • FLO11-mediated cell-surface adhesion • 1) Ras-cAMP pathway • 2) MAP kinase-dependent filamentous growth pathway • 3) The main glucose repression pathway • ( not yet known ) • 4) Target of Rapamycin (TOR) pathway – nitrogen starvation • 5) Transcription factors Sok2, Phd1, Adh1 – Epistatic pathway

  10. Fig3A. The MAPK-dependent filamentous growth pathway Ste11, Ste7 : Central kinase Msb2 : mucin-like transmembrane protein Mep2: Ammonium permease

  11. Fig3B. The Ras/cAMP/PKA pathway Cyr1 : adenylatecyclase PKA: Protein kinase A complex Sfl1: Suppressor of flocculation

  12. Fig3B. The main glucose repression pathway Hxt : Hexose transporters Hxk: Hexokinases Sfl1: Suppressor of flocculation

  13. Controlled epigenetically • 1) Cells regulary switch between the states ( transcribed <-> silent ) • 2) Stochastic switching mechanism ( Nonsense mutation ) • 3) Chromatin remodeling • Goals of adhesins silencing • 1) Balance between adhering, colonizing cells and non-adhering cells • 2) Proactively anticipate new conditions in fluctuating environments • 3)Allowing them to adhere to specific surfaces only • 4) Different subsets may allow evasion of the host immune system

  14. Recombination of Intragenic repeats ; Novel adhesins • Fastest expanding group of paralogues in the genomes • The driving force behind the creation of novel adhesins • 1) Trigger frequent slippage, recombination events • - Longer adhesins generally confer greater adherence • 2) Recombination events between repeats of different genes • - Generate chimeirc forms

  15. Fig4. Box plot of the S. cerevisiae FLO1 nucleotide sequence

  16. Conclusion • Fungal adhesion is an unusually complex and variable phenotype • 1) Quickly adapt their adhesive properties to a particular environments • 2) Many different genetic and epigenetic signaling cascades • 3) The internal tandem repeats trigger frequent recombination events • For Industrial applications, the instability of the flocculation profile is a true nightmare • Recombinant DNA techniques • For Medical applications, the remarkable plasticity of fungal adhesion also causes concern • Targets for new drugs

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