Antimicrobial peptide antibiotics inhibit aerobic denitrification via affecting electron transportation and remolding carbon metabolism

The harmful effects of antibiotics on biological denitrification have attracted widespread attention due to their excessive usage. Polymyxin B (PMB) as the typical antimicrobial peptides having been regarded as the "last hope" for treatment of multidrug-resistance bacteria, has also been detected in wastewater. However, little is known about the influence of PMB on aerobic denitrification. In this study, the impact of PMB on aerobic denitrification performance was investigated. Results showed 0.50 mg/L PMB decreased nitrate removal efficiency from 97.4% to 85.3%, and drove denitrifiers to transform more nitrate to biomass instead of producing gas-N. The live/dead staining method showed PMB damaged bacterial membrane. Transcriptome analysis further indicated the key enzymes participating in denitrification and aerobic respiratory chains were suppressed by PMB. To resist the PMB stress, denitrifiers formed thicker biofilm to protect cells from PMB damaging and thus remodeling the central carbon metabolism. Further investigation revealed denitrifiers have different preference on various carbon sources when PMB is present. Subsequently, the underlying mechanism of the distinctive carbon sources preference was explored by the combination of transcriptome and metabolism analysis. Overall, our data suggested denitrifiers have distinctive carbon sources preference under PMB treatment conditions, reminding us that carbon source selection should be cautious in practical applications.