Thermodynamics of Bacterial Energetics

Predicting which links of biogeochemical processes driven by microbes, predominate under given natural conditions requires understanding of the energetics of dissimilatory metabolism. There are two aspects of the problem to discuss  

Kinetic constraints suggest that certain processes, which are possibly based on thermodynamics, do not occur spontaneously since ahigh activation energy is needed. 

thermodynamic considerations alone would imply that oxidation ofN2 with O2 could provide a possible way of making a living for bacteria. However, the N=N bond is strong so the process requires considerable activation energy and is therefore not realized (Fenchel et al, 1998). 

A brief discussion of thermodynamics of bacterial energetics is possible on a basis of equilibrium considerations. These are for several reasons only approximate, but they do provide a heuristic insight with respect to the distribution of different types of bacterial metabolism in biogeochemical food webs. Much more detail can be found in T. Fenchel et al (1998). 

The standard free energy (A G ) of a given process can be calculated from the free energy of formation according to  

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