A fungus-bacterium co-culture synergistically promoted nitrogen removal by enhancing enzyme activity and electron transfer

The fungus Penicillium citrinuin WXP-2 and the bacterium Citrobacter freundii WXP-9 were isolated and found to have poor denitrification performance. Surprisingly, co-culture of the two strains which formed fungus-bacterium pellets (FBPs) promoted the removal efficiency of nitrate (NO3- -N 95.78%) and total nitrogen (TN; 81.73%). Nitrogen balance analysis showed that excess degraded NO3--N was primarily converted to N-2 (77.53%). Moreover, co-culture increased the dry weight to 0.74 g, The diameter of pellets and cell viability also increased by 149 and 178 times, respectively, indicating that the co-culture exerted a synergistic effect to promote growth. The increase in electron-transmission system activity [99.01 mg iodonitrotetrazolium formazanl(g.L)] and nitrate reductase activity [8.65 mg N/(min.mg protein)] were responsible for denitrification promotion. The FBPs also exhibited the highest degradation rate at 2:1 inoculation ratio and 36 h delayed inoculation of strain WXP-9. Finally, recycling experiments of [BP demonstrated that the high steady TN removal rate could be maintained for five cycles. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The co-culture of fungus and bacteria showed a synergistic effect in promoting the efficient removal of nitrate and total nitrogen, mainly through the conversion of N-2 for denitrification. The co-culture increased pellet growth and cell viability, enhanced electron-transmission system activity and nitrate reductase activity, and maintained a high steady TN removal rate for five cycles.