Kinetics of microbial respiration

In this thesis I develop a thermodynamically consistent rate law for microbial respiration. Previous approaches to predicting the rate of microbial respiration have relied on empirical relations, such as the Monod and dual-Monod equations, which do not consider how energy available in cell's environment or the accumulation of reaction products affects respiration rate. I derive a new rate law on the basis of nonlinear nonequilibrium thermodynamics and chemiosmotic theory. In this way, I am able to account for the effect of the thermodynamic driving force, the difference between the energy available in the environment and that saved by electron transport phosphorylation, on respiration rate. The new rate law also incorporates a number of factors, such as the concentrations of electron donor, acceptor, and end product species, involved in microbial respiration. The new law gives respiration rate as the product of three terms, one describing electron donation, one acceptance, and a third accounting for the thermodynamic driving force. The new rate law can be simplified under specific conditions to the various empirical rate equations in common use today. Due to its generality, the new rate law can predict the rate of both mictochondrial and microbial respiration over a spectrum of chemical conditions, offering the potential for extrapolating laboratory studies to the natural environment. Application of the new rate law to describe microbial metabolism in the geochemical environment shows that thermodynamics may control the rates of metabolisms such as sulfate reduction and methanogenesis in nature.