Thermodynamics of organisms in the context of dynamic energy budget theory

Abstract

We carry out a thermodynamic analysis to an organism. It is applicable to any type of organism because (1) it is based on a thermodynamic formalism applicable to all open thermodynamic systems and (2) uses a general model to describe the internal structure of the organism--the dynamic energy budget (DEB) model. Our results on the thermodynamics of DEB organisms are the following. (1) Thermodynamic constraints for the following types of organisms: (a) aerobic and exothermic, (b) anaerobic and exothermic, and (c) anaerobic and endothermic; showing that anaerobic organisms have a higher thermodynamic flexibility. (2) A way to compute the changes in the enthalpy and in the entropy of living biomass that accompany changes in growth rate solving the problem of evaluating the thermodynamic properties of biomass as a function of the amount of reserves. (3) Two expressions for Thornton's coefficient that explain its experimental variability and theoretically underpin its use in metabolic studies. (4) A mechanism that organisms in non-steady-state use to rid themselves of internal entropy production: "dilution of entropy production by growth." To demonstrate the practical applicability of DEB theory to quantify thermodynamic changes in organisms we use published data on Klebsiella aerogenes growing aerobically in a continuous culture. We obtain different values for molar entropies of the reserve and the structure of Klebsiella aerogenes proving that the reserve density concept of DEB theory is essential in discussions concerning (a) the relationship between organization and entropy and (b) the mechanism of storing entropy in new biomass. Additionally, our results suggest that the entropy of dead biomass is significantly different from the entropy of living biomass.

Dynamic energy budget theory restores coherence in biology

“…We need surface areas L 2 for food uptake and volumes V ¼ L 3 for maintenance; we treat the volume-specific structural mass [M V ]; M V /V as a constant (strong homeostasis). The mass description allow us to deal with mass conservation, the energy description with energy conservation and the entropy description (not presented in table 6) with irreversibilities (Sousa et al 2006). Entropy balances can only be made when energy balances are known, which in their turn can only be made when mass balances are known.…”

“…In an attempt to be explicit on consistency with empirical observations (criterion 2, table 1), we organized generally observed patterns in empirical data on various aspects of energetics, life stages and stoichiometry in tables 2 and 3 (Sousa et al 2006). DEB theory has an explanation for each of them.…”

Integrating dynamic energy budget (DEB) theory with traditional bioenergetic models

“…We have already noted the potential importance of changes in the theory that are required to cover anaerobic processes (Childress and Somero, 1990), and we have discussed situations where mechanical work represents a significant contribution to the energy budget. Both situations require extensions of the thermodynamic underpinnings of DEB theory (Sousa et al, 2006).…”

“…Relating Kooijman's DEB model to bioenergetic data is greatly facilitated by the work of Sousa et al (Sousa et al, 2006). These authors placed Kooijman's DEB model in a rigorous thermodynamic framework.…”

“…They propose that entropy changes within an aerobic organism are likewise small, implying that the chemical transformations of an aerobe in the DEB model simply involve conversion of Gibbs energy to heat. They also highlight subtleties [see table 2 of Sousa et al (Sousa et al, 2006)], not included in the current brief summary, that arise when considering anaerobic processes. Each of these considerations may be relevant when integrating information from bioenergetic data into DEB models.…”