Stoichiometric Metabolic Modelling of Nitrate Reducing Sulfur Oxidizing Bacteria for Wastewater Application

Despite the vital role of S- and N-atoms in life, some reduced inorganic sulfur compounds (RISCs) and several Ncompounds such as nitrate released into environment have detrimental e↵ects on human health and ecosystems. These compounds therefore should be removed or transformed into less toxic products. Nitrate-reducing sulfuroxidizing bacteria (NR-SOB) can effectively oxidize RISCs alongside reduction of nitrate under anaerobic condition. Purpose:Metabolic modeling of these bacteria provides insights into combination of oxidation, reduction and disproportionation reactions resulting in optimal removal performance of NR-SOB alongside production of desired products. Method:A stoichiometric metabolic model of chemolithotrophic NR-SOB was reconstructed which consisted of main metabolic pathways, sulfur metabolisms and nitrate denitrification reactions as given in KEGG, and Metacyc sources. To investigate the oxidation-reduction system under di↵erent conditions, intracellular metabolic fluxes were estimated by applying metabolic flux analysis using Cobra-toolbox v۳.۰ in MATLAB platform ۲۰۲۰a.Result:Results showed that sulfide (a completely reduced S-compound), among the four examined S-compounds, led to the highest specific growth rate with sulfate and molecular nitrogen as products. Increasing role of disproportionation reactions beside oxidation-reduction metabolism also resulted in more amassed biomass of NR-SOB. Nitrate uptake rate had a substantial influence on S-products distribution due to shifting of sulfur metabolism. Moreover, decreasing the flux of S-compound to nitrate ratio (S/NO۳) from an optimized level in each S-substrate led to incomplete denitrification and toxic gases such as NO or N۲O were produced during the process.Conclusion:Simulation of NR-SOB using this stoichiometric metabolic model provided insight to simultaneous oxidation of S- and reduction of N-compounds and can have generic application in biological removal of sulfur and nitrate contaminants in industrial wastewater.

کلیدواژه ها:

Denitrification ، FBA ، Metabolic modeling ، Sulfur-oxidizing bacteria ، Nitrate-reducing bacteria