Life is almost always associated with the generation of heat. Thus far, all chemotrophic life forms that have been studied in calorimeters were found to be exothermic. Certain literature reports have even cast doubt on the existence of endothermic growth, even though thermodynamic principles do not rule it out. The present report describes the first experiments demonstrating the actual existence of chemotrophic life forms that take up heat rather than produce it. HEAT GENERATION AND THE DRIVING FORCE FOR MICROBIAL GROWTHHeat exchange between living cells and their environment is a universal phenomenon. Life is almost always associated with the generation of heat. This is already evident in expressions in everyday language: We tend to refer to the "warmth" of living things as opposed to the "cold inanimate world". Although from a scientific point of view there is no reason why organisms could not absorb heat and thus cool down their environment [1], the actual existence of endothermic chemotrophic growth has been considered unlikely [2][3][4] in the scientific literature. More recently, Heijnen and van Dijken [5] have, however, predicted on the basis of a theoretical energy balance that acetotrophic methanogenesis could be a net heat-uptake process.The driving force for microbial growth is the change of Gibbs energy occuring in the growth medium as a result of microbial metabolism. Growing microorganisms consume high Gibbs energy foodstuffs and release waste products of low Gibbs energy. It can be shown that the decrease of Gibbs energy resulting from this exchange of metabolites reflects the total rate of entropy production generated by all the irreversible processes that make life and growth possible:(1) On average, the products must have a lower Gibbs energy than the substrates, even though one of the "products" of metabolism is new biomass.The driving force for growth is thus the dissipation of Gibbs energy and may be described as a ∆G for the overall growth reaction. It must be negative for growth to occur. The heat release of the growth reaction depends on the respective ∆H value. Although, as already pointed out, there is no thermodynamic constraint that would prevent ∆H from being positive, it is negative in an overwhelming majority of cases and thus contributes to the driving force according to (2) *Plenary lecture presented at the 16
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.