Phenotypic adaptation to freeze-thaw stress of the yeast-like fungus Geotrichum candidum.
The effect of cold stress on Geotrichum candidum was investigated at chill and freezing temperatures. Specific growth rates were determined at various temperatures and plotted according to the Ratkowsky and Arrhenius equations. The obtained profiles led to the determination of characteristics including the activation energy and notional minimum temperatures. At temperatures below the optimum single linear slopes were observed. At freezing temperatures, the loss of viability of cell populations was proportional to the number of freezing-thawing cycles. Nevertheless, the ability of G. candidum to survive this challenge depended on the physiological conditions prior to the freezing stress. The loss of viability was growth phase specific. Cells harvested in stationary phase showed a higher resistance compared to those obtained with cells in exponential phase. Furthermore, the cells of G. candidum could be adapted to the freeze-thaw challenge by pre-treatment at chill temperatures. This phenomenon known as cryotolerance was a function of the duration of the preincubation exposure.
Thammavongs
B
B
Laboratoire de Microbiologie Alimentaire, Universitá de Caen-Basse Normandie, Esplanade de la Paix, Caen France. thammavongs@ibba.unicaen.fr
Panoff
J M
JM
Guéguen
M
M
D000222:Adaptation, Physiological; D003080:Cold Temperature / Q000009:adverse effects*; D005516:Food Microbiology; D005615:Freezing; D005848:Geotrichum / Q000254:growth & development*; D010641:Phenotype; D013997:Time Factors