Design, calibration and testing of a novel isothermal calorespirometer prototype.

• An established respirometer can be expanded with calorimetric functions. • The resulting innovative calorespirometer is suited for the study of microbial growth reactions. • Despite its simple design, it achieves heat losses of 30 % and response times of 6 min. • Yeast experiments highlight the capability to differentiate metabolic pathways. A prototype of an innovative isothermal calorespirometer was developed to measure simultaneously heat production rate (calorimetry) and CO 2 evolution rate (respirometry) in real-time in a static batch vessel system. The relationship between these two variables forms the calorespirometric ratio, which serves as a crucial indicator for metabolic processes and allows for the differentiation of various metabolic pathways in simple (pure culture) and complex (e.g. soil) biological systems. The heat production rate is gauged by a thermoelectric generator situated at the bottom of the measuring channel (calorimetric unit), while the CO 2 evolution rate is monitored through a conductometric cell fixed on the lid of the channel (respirometric unit). The prototype is designed with a twin configuration, featuring both sample and reference channels. The spatial separation of the calorimetric and respirometric measuring units ensures the simultaneous measurement of the two rates from a single sample without the occurrence of crosstalk effects between the signals. The electrical calibration of the calorimetric unit reveals heat losses (approx. 30 %) and response times (approx. 6 min) that are comparable to those of established isothermal calorimeters. In parallel, growth experiments conducted with baker's yeast demonstrate the applicability of the calorespirometer prototype to biological systems. [Display omitted] [ABSTRACT FROM AUTHOR]