Introduction: The flux-force relationship between free energy dissipated during growth (∆Gmet) and microbial growth rate (µ) is often postulated. Temperature has also a strong influence on growth rate, which exhibits a non-monotonic behavior with a temperature at which the growth rate is maximum. We therefore questioned if changes in microbial growth rate associated to different temperature is sustained by a change in free energy dissipation. For that, we grew aerobically Escherichia coli K12 NCM3722 strain (∆motA), in minimal medium (Modified MOPS culture with 6 amino acids) containing glucose as the sole energy source in an isothermal calorimeter. Indeed, for aerobic metabolism, ∆Gmet mainly results from heat (∆Hmet) and isothermal calorimetry is a useful tool to monitor jointly microbial growth rate and total heat evolution. Materials and methods: Calorimetric experiments were performed with isothermal titration calorimeter connected to a specific software for controlling, acquiring, and processing data. The setup enabled real-time monitoring of sample temperature and heat flow with thermograms. Overnight grown precultures of E. coli were mixed with growth media. The initial quantity of inoculum to be transferred into calorimetric cells was precisely determined to allow a sufficiently long lag phase to allow stable thermal equilibrium before the onset of the growth process. The temperature range of calorimetric experiments varied between 28-44°C with a 1°C step and at least three replicated cultures for each temperature. Thermal profiles were normalized to calculate power vs time curves at each temperature. Heat profiles were integrated to determine heat evolution at each temperature. The exponential parts of heat evolution curves were used to estimate corresponding µmax values. Results and discussion: Evaluation of power curves showed that the µmax vs T curve exhibits the characteristic hump shaped behavior with a temperature optimum of 42°C. The heat exchanged during microbial growth ranged between 420 to 568 mJ with standard deviations from 10 to 23%. Statistical analysis of variance indicated that there was no significant difference between heat measurements at different temperatures. Therefore, our results open the debate on the precise thermodynamic driving force for microbial growth and call for further detailed investigations.