Stoichiometric Metabolic Modelling of Chemolithotroph SOB for Oxidation of Reduced Inorganic Sulfur Compounds

Reduced inorganic sulfur compounds (RISCs), released into environment as waste of industrial activities, are toxic and hence their removal from ecosystems is essential. Oxidation of these S-compounds by chemolithotroph sulfur-oxidizing bacteria (SOB) is one of benign removal methods. Metabolic modeling of this microorganism provides insights into the combination of enzymatic oxidation and disproportionation reactions which could improve the removal behavior of SOB and the manufacturing of better products. After reconstruction of a stoichiometric model in this study, flux balance analysis (FBA) was applied to estimate the intracellular metabolic fluxes and analyzing the behavior of the oxidation system. The results showed that the growth rate of microorganism was optimized when sulfide (a completely reduced S-compound) was used as substrate and sulfate produced as product. A mixture of oxidation and disproportionation reactions also led to an increase in the biomass of SOB. Moreover, an investigation of oxygen uptake rate on growth and products formation displayed that oxygen had a significant influence on S-product distributions due to shifting sulfur metabolism. This stoichiometric metabolic model could simulate the oxidation of S-compounds by chemolithotroph SOB and can have generic application biological removal of sulfur contaminant in addition to bringing insight to modification of industrial processes.