Flocculation onset in Saccharomyces cerevisiae: effect of ethanol, heat and osmotic stress.
OBJECTIVE
To examine the effect of different stress conditions on the onset of flocculation in an ale-brewing strain, Saccharomyces cerevisiae NCYC 1195.


RESULTS
Flocculation was evaluated using the method of Soares, E.V. and Vroman, A. [Journal of Applied Microbiology (2003) 95, 325]; plasma membrane integrity was accessed using propidium iodide and the staining of the yeast cell wall was performed using calcofluor white M2R. Cells in exponential phase of growth were subjected to different stress conditions. The addition of 1%, 3% and 5% (v/v) ethanol, 1% and 3% (v/v) isopropanol or a brief heat shock (52 degrees C, 5 min), did not induce an early flocculation phenotype when compared with control cells. The addition of 10% (v/v) ethanol, a continuous mild heat-stress (37 degrees C) or an osmotic stress (0.5 or 1 mol l(-1) of NaCl) did not induce a flocculent phenotype.


CONCLUSIONS
Flocculation seems not to be induced as a response to different chemical (ethanol and isopropanol) and physical (heat and osmotic) stress conditions. Conversely, osmotic and ethanol [10% (v/v)] stress, as well as a continuous mild heat shock (37 degrees C), have a negative impact on the phenotype expression of flocculation.


CONCLUSIONS
The findings reported here contribute to the elucidation of the control of yeast flocculation. This information might be useful to the brewing industry, as the time when the onset of flocculation occurs can determine the fermentation performance and the beer quality, as well as in other biotechnological industries where flocculation can be used as a cell separation process.
Claro
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Departamento de Engenharia Química, Instituto Superior de Engenharia do Instituto Politécnico do Porto, Rua Dr António Bernardino de Almeida, 431, 4200-072 Porto, Portugal.
Rijsbrack
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Soares
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D000434:Alcoholic Beverages / Q000382:microbiology*; D002473:Cell Wall / Q000502:physiology; D003470:Culture Media; D000431:Ethanol / Q000494:pharmacology; D005427:Flocculation; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D006358:Hot Temperature; D009995:Osmosis / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000187:drug effects; D012997:Solvents / Q000494:pharmacology
D003470:Culture Media; D012997:Solvents; D000431:Ethanol