FEMS Microbiology Ecology, 96, 2020, faa002 doi: 10.1093/femsec/faa002 Advance Access Publication Date: 11 January 2020 Research Article RESEARCH ARTICLE The vertical distribution of tetA and intI1 in a deep lake is rather due to sedimentation than to resuspension Andrea Di Cesare 1, * ,† , Ester M Eckert 1,† , Camille Cottin 1,2 , Agn ` es Bouchez 2 , Cristiana Callieri 1 , Mario Cortesini 1 , Andrea Lami 1 and Gianluca Corno 1 1 CNR – IRSA Water Research Institute, Molecular Ecology Group (MEG). Largo Tonolli 50, 28922 Verbania, Italy and 2 INRA – UMR CARRTEL, 75 ave de Corzent, 74200 Thonon les Bains, France ∗ Corresponding author: CNR – IRSA Water Research Institute, Molecular Ecology Group (MEG). Largo Tonolli 50, 28922 Verbania, Italy. Tel: +39 0323 518321; E-mail: andrea.dicesare@cnr.it One sentence summary: Sedimentation of antibiotic resistance genes in lake water. † These authors contributed equally to this work. Editor: Kornelia Smalla ABSTRACT Lakes are exposed to anthropogenic pollution including the release of allochthonous bacteria into their waters. Antibiotic resistance genes (ARGs) stabilize in bacterial communities of temperate lakes, and these environments act as long-term reservoirs of ARGs. Still, it is not clear if the stabilization of the ARGs is caused by a periodical introduction, or by other factors regulated by dynamics within the water column. Here we observed the dynamics of the tetracycline resistance gene (tetA) and of the class 1 integron integrase gene intI1 a proxy of anthropogenic pollution in the water column and in the sediments of subalpine Lake Maggiore, together with several chemical, physical and microbiological variables. Both genes resulted more abundant within the bacterial community of the sediment compared to the water column and the water-sediment interface. Only at the inset of thermal stratifcation they reached quantifable abundances in all the water layers, too. Moreover, the bacterial communities of the water-sediment interface were more similar to deep waters than to the sediments. These results suggest that the vertical distribution of tetA and intI1 is mainly due to the deposition of bacteria from the surface water to the sediment, while their resuspension from the sediment is less important. Keywords: antibiotic resistance; intI1; freshwater lake; vertical column; sediment water interface; bacterial community INTRODUCTION The aquatic environment is a long-term reservoir for antibiotic resistance genes (ARGs) including those against synthetic and semisynthetic antibiotics (Allen et al. 2010; Eckert et al. 2018; Yang et al. 2018). Their diffusion can be attributed to differ- ent pollution sources, including the release of treated wastew- ater (Czekalski, D´ ıez and B ¨ urgmann 2014). In fact, wastewater treatment plants (WWTPs) are not designed to remove antibi- otic resistant bacteria (ARB) and ARGs and, where present, the fnal disinfection treatment reduces the overall bacterial load, but might select for ARGs (Di Cesare et al. 2016b). Control of the diffusion of antibiotic resistances can thus not be limited to specifc actions in hospitals and in intensive farming, but the environment should be included in the global cycle of resistance (Martinez 2009; Manaia 2017). Received: 11 March 2019; Accepted: 8 January 2020 C  FEMS 2020. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com 1 Downloaded from https://academic.oup.com/femsec/article/96/2/fiaa002/5700709 by guest on 22 October 2023