title: Trace levels of sewage effluent are sufficient to increase class 1 integron prevalence in freshwater biofilms without changing the core community.
abstract: Most river systems are impacted by sewage effluent. It remains unclear if there is a lower threshold to the concentration of sewage effluent that can significantly change the structure of the microbial community and its mobile genetic elements in a natural river biofilm. We used novel in situ mesocosms to conduct replicated experiments to study how the addition of low-level concentrations of sewage effluent (nominally 2.5 ppm) affects river biofilms in two contrasting Chalk river systems, the Rivers Kennet and Lambourn (high/low sewage impact, respectively). 16S sequencing and qPCR showed that community composition was not significantly changed by the sewage effluent addition, but class 1 integron prevalence (Lambourn control 0.07% (SE ± 0.01), Lambourn sewage effluent 0.11% (SE ± 0.006), Kennet control 0.56% (SE ± 0.01), Kennet sewage effluent 1.28% (SE ± 0.16)) was significantly greater in the communities exposed to sewage effluent than in the control flumes (ANOVA, F = 5.11, p = 0.045) in both rivers. Furthermore, the difference in integron prevalence between the Kennet control (no sewage effluent addition) and Kennet sewage-treated samples was proportionally greater than the difference in prevalence between the Lambourn control and sewage-treated samples (ANOVA (interaction between treatment and river), F = 6.42, p = 0.028). Mechanisms that lead to such differences could include macronutrient/biofilm or phage/bacteria interactions. Our findings highlight the role that low-level exposure to complex polluting mixtures such as sewage effluent can play in the spread of antibiotic resistance genes. The results also highlight that certain conditions, such as macronutrient load, might accelerate spread of antibiotic resistance genes.
authors.affiliation: NERC Centre for Ecology & Hydrology, Wallingford, OX10 8BB, UK. Electronic address: kleh@ceh.ac.uk.
authors.forename: Katja
authors.initials: K
authors.lastname: Lehmann
authors.affiliation: Imperial College London, Department of Life Sciences, Silwood Park Campus, SL5 7PY, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bell
authors.affiliation: NERC Centre for Ecology & Hydrology, Wallingford, OX10 8BB, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bowes
authors.affiliation: School of Life Sciences, University of Warwick, Coventry, UK.
authors.forename: Gregory C A
authors.initials: GCA
authors.lastname: Amos
authors.affiliation: European Centre for Environment and Human Health, University of Exeter Medical School, Knowledge Spa, Royal Cornwall Hospital, Truro, UK.
authors.forename: Will H
authors.initials: WH
authors.lastname: Gaze
authors.affiliation: School of Life Sciences, University of Warwick, Coventry, UK.
authors.forename: Elizabeth M H
authors.initials: EMH
authors.lastname: Wellington
authors.affiliation: NERC Centre for Ecology & Hydrology, Wallingford, OX10 8BB, UK.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Singer
mesh_terms: D018441:Biofilms; D032023:Integrons; D010758:Phosphorus; D015995:Prevalence; D045483:Rivers / Q000737:chemistry; D012722:Sewage / Q000737:chemistry*
chemical_list: D012722:Sewage; D010758:Phosphorus
keywords: Antibiotic resistance; Biofilms; Class 1 integron-integrase gene; River ecology; River health; Sewage effluent