Inhibition of ferrous iron (Fe2+) to sulfur-driven autotrophic denitrification: Insight into microbial community and functional genes

The effect of Fe2+ on the performance of sulfur-driven autotrophic denitrification (SDAD) using S-0 as electron donor was evaluated. The experimental results showed that as initial Fe2+ concentration increased, nitrate (NO3-) removal rate significantly decreased. Fe2+ ion (0.1 mM and 1 Mm) inhibited SDAD rate (approximately 10% and 50%) and resulted in an accumulation of nitrite (NO2-) and nitrous oxide (N2O). The relative abundance of Thiobacillus was positively correlated with NO3- removal rate, whereas negatively correlated with Fe2+ concentration, suggesting that Fe2+ inhibited the sulfur-oxidizing denitrifying bacteria. Moreover, the abundance of bacterial 16S rRNA, denitrifying genes (narG, nirS, nirK and nosZ) and sulfur-oxidizing genes (soxB and dsrA) decreased with the increase of Fe2+ concentration, among them nosZ and soxB were the most sensitive genes to Fe2+, and nosZ/narG, soxB/(bacterial 16S rRNA) and soxB/nirK had influence on NO3- removal rate, while nosZ/ (bacterial 16S rRNA) affected N2O accumulation rate.

Automated summary

The presence of Fe2+ significantly affects the performance of sulfur-driven autotrophic denitrification, with higher concentrations leading to inhibition of denitrification and accumulation of nitrite and nitrous oxide. The abundance of Thiobacillus is positively correlated with nitrate removal rate, but negatively correlated with Fe2+ concentration. Fe2+ also influences the abundance of bacterial 16S rRNA, denitrifying genes, and sulfur-oxidizing genes, particularly nosZ and soxB, which have the most sensitivity to Fe2+.