Biothermodynamics was founded in the same time, together with classical thermodynamics, by the same scientists – Lavoisier and Laplace [Lavoisier and Marquis de Laplace, 1783; Lavoisier and DeLaplace, 1994; Müller, 2010; Popovic, 2022a]. Biothermodynamics of microorganisms represents one of the youngest scientific disciplines developed in last 75 years [Morowitz, 1955, Morowitz, 1968, Morowitz, 1992; Battley, 1992, Battley, 1998, Battley, 1999b, Battley, 2013; Battley et al., 1997; von Stockar and Liu, 1999]. It represents not just application of the thermodynamic philosophical framework and tools to analysis of biological systems, but also an authentic scientific discipline laying on the intersection of biology, chemistry and (bio)physics [Von Stockar, 2013a; Von Stockar, 2013b; Von Stockar et al., 2013; Von Stockar et al., 2006; Assael et al., 2022; Von Stockar and Liu, 1999; Ozilgen and Sorgüven, 2017; Popovic, 2022b]. In contrast to biology which is divided into various relatively independent disciplines (zoology, plant science, microbiology etc.) the subject of biothermodynamics is all animate matter (from subcellular [Popovic, 2022a; Gale, 2022, Gale, 2020, Gale, 2019, Gale, 2018; Şimşek et al., 2021; Lucia et al., 2021, Lucia et al., 2020a, Lucia et al., 2020b], through unicellular [Liu et al., 2007; Duboc et al., 1999; Battley, 1999b, Battley, 1998, Battley, 1992; Popovic, 2019; Popovic et al., 2021], to multicellular [Dragicevic and Sredojevic, 2011; Popovic, 2022c; Popovic and Minceva, 2021b, Popovic and Minceva, 2020c; Balmer, 2010; Ozilgen and Sorgüven, 2017; Von Stockar, 2013a; Von Stockar, 2013b]. Moreover, the subject of biothermodynamics is not only physical and chemical characterization of organisms but also characterization of interactions and energy flows between organisms, and between an organism and its environment [Balmer, 2010; Popovic, 2022a, Popovic, 2023a].

Biothermodynamics deals with the driving forces of biological processes and mechanisms of biological processes [von Stockar and Liu, 1999; Von Stockar, 2013b; Assael et al., 2022; Battley, 1998, Battley, 1999b, Battley, 2013; Popovic, 2019]. The general thermodynamic framework is used in analyzing animate matter as thermodynamic systems interacting with its environment, performing biological processes [Barros, 2021, 2020, Barros et al., 2016; Maskow, von Stockar, 2013; Maskow and von Stockar, 2005; Maskow et al., 2010a, Maskow et al., 2010b]. Biological processes can be considered as chemical and thermodynamic processes performed by biological systems during interactions with their environment [Popovic, 2018, Popovic, 2014a, Popovic, 2014b]. For example, (micro)organism growth represents a biological, chemical and thermodynamic process that leads to the change of state of the system [Popovic, 2018, Popovic, 2017]. An organism represents an amount of substance clearly separated and bordered from its surroundings, characterized by state parameters (mass, volume, temperature, enthalpy, entropy, Gibbs energy etc.) [Von Stockar, 2013a; Von Stockar, 2013b; Assael et al., 2022]. During growth, there are changes in state parameters, which lead to change in state of the system [Popovic, 2018, Popovic, 2014a, Popovic, 2014b]. The process is led by a driving force [Von Stockar, 2013a, Von Stockar, 2013b; Assael et al., 2022]. The driving force for growth of a population of subcellular microorganisms (viruses and viroids) is Gibbs energy of biosynthesis [Popovic, 2022a; Popovic and Minceva, 2020a, Popovic and Minceva, 2020b]. The driving force for cellular organisms is Gibbs energy of growth [Von Stockar, 2013a; Von Stockar, 2013b; von Stockar and Liu, 1999; Hellingwerf et al., 1982; Westerhoff et al., 1982]. The driving force for growth of multicellular organisms is Gibbs energy of growth [Popovic and Minceva, 2021b, Popovic and Minceva, 2020c].

Thermodynamic properties have been determined for limited number of cellular microorganisms. Empirical formulas and enthalpies of some microorganism species were reported in the literature [Naresh et al., 2012; Battley, 1999b, Battley, 1998, Battley, 1992; Battley et al., 1997; Duboc et al., 1999; Gurakan et al., 1990; Guenther, 1965; Prochazka et al., 1973, Prochazka et al., 1970; Wang et al., 1976; Popovic, 2019]. Knowing empirical formulas of microorganisms is very important, since they are an important property of microbial cells [Rittmann and McCarty, 2020]. They are necessary for balancing biological reactions [Rittmann and McCarty, 2020; Popovic, 2019]. Entropies of some microorganism species have also been reported in the literature [Battley et al., 1997; Popovic et al., 2021; Popovic, 2019]. In total, empirical formulas and thermodynamic properties have been reported for more than 40 microorganism species. However, there are many species for which they have not been determined.

It has been argued that understanding and engineering microbial communities requires a holistic view that considers not only species–species, but also species–environment interactions, thermodynamic principles and feedbacks between ecological and evolutionary dynamics [Zerfaß et al., 2018; Seto and Iwasa, 2020]. Microbial communities, also known as microbial consortia, have a great potential in biotechnology [Atkinson et al., 2022; Duckner et al., 2021; Grandel et al., 2021]. Microbial consortia are able to grow on many substrates, are resistant to environmental stress and can perform of more complex functions than a single microorganism [Bhatia et al., 2018]. However, metabolic processes in microbial consortia are difficult to control [Atkinson et al., 2022; Grandel et al., 2021]. A lot of work has been made on design of microbial consortia [Atkinson et al., 2022; Duckner et al., 2021; Grandel et al., 2021]. Since interactions between organisms are governed by energy, biothermodynamics has a potential to become an excellent tool for design of microbial consortia.

Microorganisms play an important role in soil ecosystems [Barros, 2021; Barros and Feijóo, 2003; Bhanja et al., 2019; Harris et al., 2012; Zhang et al., 2021b; Schipper et al., 2014]. The thermodynamic approach allows an analysis of metabolic processes of soil microorganisms as key channels controlling the interchange of matter and energy between soil and the environment, through the concept of microbial energy use efficiency [Barros, 2021]. A method was developed to measure the efficiency of carbon utilization by soil microbes by microcalorimetry, though a combined mass and energy balance [Barros and Feijóo, 2003; Barros et al. 2020]. Calorimetry is able to measure metabolic rates of soli microorganisms through heat released by their metabolism, using small amounts of soil for the experimental measurements [Barros Pena, 2018]. Thus, thermodynamic characterization of soil microorganisms and soil organic matter would be very useful to understand their strategies for survival and role in element cycling in the soil [Barros, 2021]. However, this is hindered by lack of data on empirical formulas and thermodynamic properties of soil microorganisms and soil organic matter [Barros, 2021; Barros et al., 2023].

The aim of this paper is to determine enthalpies and Gibbs energies of five microorganism species, and their macromolecular components: nucleic acids, globular proteins and fibrous proteins. Moreover, the thermodynamic properties will be used to analyze interactions between microorganisms in mixed culture. Microbial communities represent the future research frontier. Thus, the thermodynamic background of microbial interactions can facilitate research in microbiology, biothermodynamics and biotechnology.