Microbial community functional structure in response to micro-aerobic conditions in sulfate-reducing sulfur-producing bioreactor

Limited oxygen supply to anaerobic wastewater treatment systems had been demonstrated as an effective strategy to improve elemental sulfur (S-0) recovery, coupling sulfate reduction and sulfide oxidation. However, little is known about the impact of dissolved oxygen (DO) on the microbial functional structures in these systems. We used a high throughput tool (GeoChip) to evaluate the microbial community structures in a biological desulfurization reactor under micro-aerobic conditions (DO: 0.02-0.33 mg/L). The results indicated that the microbial community functional compositions and structures were dramatically altered with elevated DO levels. The abundances of dsrA/B genes involved in sulfate reduction processes significantly decreased (p < 0.05, LSD test) at relatively high DO concentration (DO: 0.33 mg/L). The abundances of sox and fccA/B genes involved in sulfur/sulfide oxidation processes significantly increased (p < 0.05, LSD test) in low DO concentration conditions (DO: 0.09 mg/L) and then gradually decreased with continuously elevated DO levels. Their abundances coincided with the change of sulfate removal efficiencies and elemental sulfur (S-0) conversion efficiencies in the bioreactor. In addition, the abundance of carbon degradation genes increased with the raising of DO levels, showing that the heterotrophic microorganisms (e.g., fermentative microorganisms) were thriving under micro-aerobic condition. This study provides new insights into the impacts of micro-aerobic conditions on the microbial functional structure of sulfate-reducing sulfur-producing bioreactors, and revealed the potential linkage between functional microbial communities and reactor performance.