Enhanced horizontal transfer of antibiotc resistance genes in an aerated constructed wetland

CAMILA KNECHT; MARKUS KRÜGER; ARIF AHMED; SIMON KELLMANN; INES MÄUSEZAHL; MONIKA MÖDER; HEINZ KÖSER; OLAWALE. O. ADELOWO; JAIME NIVALA; JOCHEN A. MÜLLER

Aarhus

Simposio; 8th International Symposium on Wetland Pollutant Dynamics and Control WETPOL 2019; 2019

Wastewater treatment systems are known to release antibiotic resistant bacteria (ARB) into the environment. Treated  wastewater often contains novel ARB in addition to those types present already in the influent wastewater. Antibiotic resistance genes (ARG) can be transferred between various bacteria in the sewage mixture. Wastewater treatment systems have hence been coined as "breeding grounds" for ARB. The driving forces for ARG transfer are unclear. It has been questioned whether antibiotics themselves, typically present only at sub-inhibitory concentrations in wastewater, constitute a selective pressure for acquisition and maintenance of resistance genes. An alternative mechanistic explanation is that gene transfer is induced by cellular stress. In this study, we investigated the effect of aeration in a pilot-scale constructed wetland (CW) on the fate of indicator ARG as well as class 1 integron, which is an important mobile carrier of ARG. A non-aerated CW was investigated in parallel as reference. Both CW received pre-treated wastewater from the same source. In addition to measuring standard wastewater parameters, we quantified concentrations of the antibiotics  sulfamethoxazole (SMX) and trimethoprim (TMP) by LC-MS, enumerated abundances of sul1p { margin-bottom: 0.1in; line-height: ,sul2,dfrA1, intl1, uidA and 16S rRNA gene copies by qPCR, and carried out ARG host profiling by cultivation-dependent means.  Overall, ARG numbers were significantly reduced in both wetlands, with the aerated system achieving a greater reduction. However, the abundance of some ARG and class 1 integrons were observed to increase within the aerated wetland. Since SMX and TMP were present only at very low concentrations in both CW, this increase suggests that environmental stress factors may influence the abundance of ARG, depending on their genetic context. Cultivation-dependent and cultivation-independent quantification of Escherichia coli suggested that this important carrier of ARG is under stress in the aerated CW. Thus, using CW as model systems, our results indicate that aeration during wastewater treatment drives horizontal transfer of mobile ARG.