The metabolic profile of lag and exponential phases of Saccharomyces cerevisiae growth changes continuously

Cellular growth is usually separated in well-defined phases. For microorganism like Saccharomyces cerevisiae, two phases usually defined are (1) a lag phase, in which no growth is observed and cells adapt to a new environment, followed by (2) an exponential phase, in which rapid proliferation occurs. Here we investigate whether these well-defined phases are uniform. By using flow-microcalorimetry, we found that the metabolic profile of the culture is continuously changing, both in the lag and exponential phases of growth. Along the lag phase there is a continuous increase in the energy that is dissipated irreversibly as heat, while in the exponential phase the opposite occurs. We also confirm recent observations that the oxidative component of metabolism decreases along the exponential phase. Interestingly, nutrient limitation further decreases the amount of energy that is dissipated irreversibly. Altogether, this points to a picture in which cells respond rapidly to minute environmental changes by adjusting their metabolic profile.