MONITORING SYNCHRONIZED OSCILLATING YEAST CULTURES BY CALORIMETRY

Synchronized oscillating cultures of Saccharomyces cerevisiae CBS 426 exhibit periodic oxido-reductive metabolism. The changing metabolism is detectable by in situ heat-flux calorimetry in the BSC 81, which was operated as a chemostat in these experiments. The measured metabolic heat flux oscillated in phase and with the same period as the other monitored process variables (CER, OUR and Do) at the dilution rates studied (0.12 and 0.14 h-1). There was a difference of 2 W l-1 between the minima and maxima of the oscillating heat flux. During these synchrony oscillations, the proportionality constant between heat dissipation and oxygen consumption was not constant, but reached a maximum value during each cycle. Data gathered from a separate experiment with the same strain in a standard laboratory bioreactor (D = 0.071 h-1) clearly corroborated the biological nature of the oscillations. The oscillatory character of metabolism is none other than a reflection of the cell cycle, which is punctuated by specific landmark events. Based on these results, we propose a correlation between the heat dissipation and the specific cell cycle classes.