Impact of nitrate addition on the resistome and mobilome from a full-scale sewer

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2022-07, Vol.439, p.135653, Article 135653
• Main Authors: Gionchetta, Giulia, Fillol, Mireia, López, Noelia, Kassotaki, Elissavet, Sànchez-Melsió, Alexandre, Gutiérrez, Carmen, Gutiérrez, Oriol, Luis Balcázar, José, Borrego, Carles M.
• Format: Article
• Language: English
• Subjects: Mobilome; Nitrate dosing; Resistome; Sewer biofilms; Stress response
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2022.135653

[Display omitted] •Effects of nitrate on sewer biofilms are maximal at the dosing site.•Clear differences were observed in the sewer resistome and mobilome along the pipe.•The WWTP inlet has a richer and more diverse resistome and mobilome.•The effect of nitrate vanishes with distance to the dosing site.•Dosing chemicals in sewers may increase the burden of biological pollutants in WWTP. Oxidative chemicals, such as nitrate, are periodically added to sewer systems to mitigate sulfide production and its accumulation but data are lacking on how these treatments affect sewage microbiota and alter their gene expression and mobilization. The present study investigated such effects on the biofilm of a full-scale sewer collected at two different locations, namely a pumping station and at the inlet of an urban wastewater treatment plant (WWTP), before and 15 days after nitrate dosage using a combination of culture-dependent and -independent approaches. Nitrate dosing resulted ineffective on the concentration of antibiotic-resistant Escherichia coli (AR-EC) in biofilms but greatly affected the composition of biofilm bacterial communities and the associated resistome and mobilome, especially at the pumping station where nitrate was dosed. Such responses consisted of a clear reduction on strict anaerobes; an almost twofold increase on the expression of recA gene (stress-response marker); and a significant increase on the relative abundance of most antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). In turn, the effects of nitrate dosing at the WWTP inlet were barely visible, suggesting that they vanished into the distance from the pumping site (2.4 km). Remarkably, however, the relative abundance of both resistance and mobilization gene biomarkers at the inlet of the studied WWTP clearly oversized that at the pumping station confirming that these facilities are sinks where these resistance determinants accumulate and propagate. Considering the abundance of resistant bacteria and genes in urban sewage, the effects of dosing chemicals should be carefully assessed to lessen the load of such biological pollutants into WWTPs.