Response of immobilized denitrifying bacterial consortium to tetracycline exposure

Tetracycline (TC) as one of the most widely used antibiotics commonly exists in aquaculture tail water and piggery wastewater, causing risks to human. However, the response of immobilized anaerobic denitrifying bacterial consortium to TC exposure lacks systematic research. In this study, the denitrification performance and the compositional shift of extracellular polymeric substances (EPS) and microbial community under TC stress were investigated. The inhabitation effect of TC on nitrate reduction of the immobilized bacterial consortium became evident at high concentrations (50 mg/L and 100 mg/L). Nitrite reduction was more sensitively inhibited than nitrate reduction. The inhabitation effect was mainly due to the fact that TC damaged cell membranes and subsequently effect the intracellular enzymes activities relating to denitrification (NAR and NIR activities). About 50% of TC can be removed by the immobilized bacterial consortium under all tested TC concentrations. Threedimensional excitation-emission matrix (3D-EEM) results implied that the tryptophan like substances of EPS were obviously quenched with increasing TC concentration. EPS played an important role in TC removal. The denitification performance of the immobilized bacterial consortium under TC stress was attributed to the genera Paraccoccus, Pseudoxanthomonas, Diaphorobacter and Pseudomonas. Initial TC concentration obviously affected the microbial communities. This study may facilitate the management of aquaculture tail water and piggery wastewater contaminated with nitrate and antibiotics.

Automated summary

This study investigated the denitrification performance and compositional shift of extracellular polymeric substances (EPS) and microbial community in an immobilized anaerobic denitrifying bacterial consortium under tetracycline (TC) stress. High concentrations of TC inhibited the nitrate reduction ability of the bacterial consortium, with nitrite reduction being more sensitive to inhibition. The inhibitory effect was mainly due to TC damaging cell membranes and affecting intracellular enzymes activities. Approximately 50% of TC was removed by the bacterial consortium, with EPS playing an important role in TC removal. The denitrification performance of the consortium under TC stress was attributed to specific bacteria genera. The initial TC concentration significantly affected the microbial communities.