Accelerating denitrification and mitigating nitrite accumulation by multiple electron transfer pathways between Shewanella oneidensis MR-1 and denitrifying microbial community

The bio-denitrification was usually retarded by the unbalance of electron generation and consumption. In this study, mixing S. oneidensis MR-1 with denitrifying microbial community increased the nitrogen removal rate by 74.74 % via the interspecies electron transfer (IET), and reduced the accumulated nitrite from 9.90 +/- 0.81 to 0.02 +/- 0.03 mg/L. Enhanced denitrification still appeared but relatively decreased, when S. oneidensis MR-1 was separated by a dialysis bag (MW < 3000), indicating mediated interspecies electron transfer (MIET) counted in IET. The results of electron transfer activity and sludge conductivity suggested DIET and MIET jointly transfer electrons from MR-1 to electroactive denitrifying bacteria (EDB), improving denitrifying reductase activities. Electron distribution among denitrifying reductases was found to be associated with the IET rate. Microbial insights showed the total abundance of EDB was increased, and denitrifying genes were correspondingly enriched. Pseudomonas was found to cooperate with exoelectrogens in a complicated microbial community.

Automated summary

This study found that the use of S. oneidensis MR-1 in combination with denitrifying microbial community can significantly enhance the bio-denitrification process through interspecies electron transfer (IET). The nitrogen removal rate was increased by 74.74% and the accumulation of nitrite was greatly reduced. The results also indicated that mediated interspecies electron transfer (MIET) played a role in enhancing denitrification, as observed when S. oneidensis MR-1 was separated by a dialysis bag.