Screening of sulfur-reducing bacteria an‎d analysis of their metabolic fluxes

10/20/2026 12:00:00 AM

Given the importance of sulfate-reducing bacteria (SRB) in the bioremediation of wastewaters, this study focused on their screening from wastewater samples an‎d on the analysis of their metabolic fluxes. The research was conducted in two sections: an experimental part an‎d a metabolic modeling part. In the experimental section, three wastewater sources — the Tabriz leather industry, the Sarein sulfur hot spring, an‎d Babagorgor Lake in Qorveh — were examined. The results showed that the leather industry effluent exhibited the highest performance, achieving 71.95% sulfate removal an‎d 51.51 ppm elemental sulfur production within 8 days. The higher concentration of organic compounds an‎d the presence of Fe2+ ions enhanced electron transfer an‎d accelerated reductive pathways, whereas in the Sarein sample, due to its simpler composition an‎d limited organic substrates, sulfate removal reached only 39.72%. The faster increase in pH an‎d higher biomass growth in the leather effluent indicated a higher metabolic activity of SRB. Microscopic observations also confirmed the presence of Gram-negative, rod-shaped bacteria. In the modeling section, the genome-scale metabolic model of Desulfovibrio vulgaris Hildenborough comprising 1,014 reactions, 948 metabolites, an‎d 744 genes was employed. Flux analysis results showed that under heterotrophic conditions with a fixed lactate uptake rate of −10 mmol/gDWh, increasing sulfate uptake caused a metabolic shift from incomplete to complete oxidation, an‎d the maximum growth rate of 0.6845 h⁻¹ was achieved at a sulfate uptake rate of 0.1731 mmol/gDWh. The results indicated that an appropriate balance between carbon sources an‎d sulfate is a determining factor in regulating the trade-off between complete an‎d incomplete oxidation pathways. Under H2S-maximizing conditions, the consumed lactate was almost entirely directed toward sulfate reduction to sulfide (up to 11 mmol/gDWh), while cell growth was halted, indicating that H2S production occurs independently of biomass formation. Under autotrophic conditions, in the presence of H2, acetate, an‎d CO2 (mixotrophy) without substrate limitation, sulfate reduction occurred simultaneously with cell growth; however, the removal of acetate resulted in complete growth inhibition, highlighting the essential role of acetate in maintaining redox balance. Reducing sulfate uptake led to decreased hydrogen consumption, increased utilization of organic an‎d inorganic carbon sources, an‎d lower sulfide production. At a sulfate uptake rate of 1.4751 mmol/gDWh, maximum growth was achieved; further reduction in sulfate uptake decreased carbon consumption, thereby reducing growth an‎d eventually stopping sulfide production. Overall, the findings demonstrate the high metabolic flexibility of SRB in regulating cellular energy an‎d electron balance, providing a basis for targeted metabolic engineering strategies to optimize sulfate removal an‎d biological H2S production in industrial bioremediation systems.

باكتري‌هاي احياكننده سولفات , انتقال الكترون , هتروتروفي و اتوتروفي , تصفيه زيستي

Sulfate reducing bacteria , Electron transfer , Heterotrophy an‎d Autotrophy , Bioremediation of wastewater

Leili Doosti

Fereshteh Naeimpoor