Vavilin, V.A., Lokshina, L.Y. Application of Basic Isotope Equations to Describe the Dynamics of Microbiological Processes: Deuterium Redistribution. BIOPHYSICS 67, 931–942 (2022)
Basic isotope dynamics equations based on maintaining deuterium equilibrium were used to analyze the dynamics of nitrite-dependent anaerobic methane oxidation (NDAMO) in two laboratory experiments with different initial substrate concentrations and deuterium isotope variables. Notably, the initial amount of water in a closed vessel was reduced by a factor of about 2.8 in the second experiment. According to the model, methane was completely consumed, while nitrite ions were still present in excessive amounts at the end of the first experiment and methane was present, while nitrite ions were completely exhausted at the end of the second experiment. Concentrations of the substrates containing a single deuterium atom (СН4 and NH), the product (Н2О), and the biomass of anaerobic methanotrophic (ANME) microorganisms (C5H7NO2) were taken as isotope variables in the model. Stoichiometric reaction equations were derived to describe the redistribution of deuterium between the reaction substrates, product (water), and biomass. Isotope fractionation was shown to proceed in the course of a microbiological reaction in water. As a result, the substrates become enriched in deuterium, while water and the biomass become depleted of deuterium. The fractionation process ended after t ≥ 17 h in the first experiment, which was accompanied by a slight drop in deuterium in the biomass water. In the second experiment, fractionation ended after t ≥ 140 h, the deuterium content decreased significantly in both water and the biomass, and its decrease depended on the initial concentration of deuterium-containing water. This was due to dilution of the water in the vessel with deuterium-depleted water generated in the NDAMO process. The paper additionally summarizes the results of modeling the dynamics of 11 biological processes in a long-term study, in which stable carbon isotopes have mainly been measured. Isotope fractionation factors used in the simulation were described.