Microbial community structure and function in response to the shift of sulfide/nitrate loading ratio during the denitrifying sulfide removal process

Influence of acetate-C/NO₃^--N/S^2- ratio to the functional microbial community during the denitrifying sulfide removal process is poorly understood. Here, phylogenetic and functional bacterial community for elemental sulfur (S⁰) recovery and nitrate (NO₃^-) removal were investigated with the switched S^2-/NO₃^- molar ratio ranged from 5/2 to 5/9. Optimized S^2-/NO₃^- ratio was evaluated as 5/6, with the bacterial genera predominated with Thauera, Enterobacter, Thiobacillus and Stappia, and the sqr gene highly expressed. However, insufficient or high loading of acetate and NO₃^- resulted in the low S⁰ recovery, and also significantly modified the bacterial community and genetic activity. With S^2-/NO₃^- ratio of 5/2, autotrophic S^2- oxidization genera were dominated and NO₃^- reduction activity was low, confirmed by the low expressed nirK gene. In contrast, S^2-/NO₃^- ratio switched to 5/8 and 5/9 introduced diverse heterotrophic nitrate reduction and S⁰ over oxidization genera in accompanied with the highly expressed nirK and sox genes.