Aims: To investigate the stress response during nutrient deprivation, particularly with regard to the application of phenol as growth substrate of Pseudomonas putida with calorimetric measurements as a new method. Methods and Results: The online and noninvasive measurement of the thermal power P-0 permits the detection of microbial activity during the starvation period. While the results of the investigations with phenol reveal a significant loss of activity as a function of the temporal nutrient dosage, only a small loss of activity was detected by using glucose. Microbiological methods (colony forming units (CFU) and activity of catechol-2,3-dioxygenase) showed a loss of the enzyme activity at a constant CFU. The introduction of a simple decay parameter k(D) in the kinetic description of the growth process on phenol was sufficient for the successful kinetic modelling. Conclusions: The combination of calorimetric measurements and the determination of the enzymatic activity proved the loss of activity of Ps. putida during the deprivation of the substrate phenol. Significance and Impact of the study: The initial heat power (P-0) proves to be a suitable parameter for the characterization of the physiological state of the culture and can be used for the regulation of nutrient supply in biotechnological process development.