Wastewater treatment bioreactors, including attached growth systems that use biofilms to remove organic matter and nutrients from wastewater, harbor antibiotic resistance genes (ARGs). Biofilms are known to be spatially heterogeneous due to variations in environmental conditions with depth, but little is known about depth stratification of ARGs or mobile genetic elements associated with horizontal gene transfer of ARGs in wastewater treatment biofilm reactors. To address this knowledge gap, we quantified distribution by depth of four ARGs (sul1, tetW, ermB, and qnrS) and the integron intI1, as well as alpha and beta diversity, in biofilms from a lab-scale rotating annular reactor (RAR). The RAR was fed synthetic wastewater containing trace concentrations of antibiotics similar to those observed in full-scale WWTPs. Once the biofilms were established, coupons containing biofilms were cryosectioned into layers representing different depths, and subjected to qPCR measurement of abundances ofARGs and intI1. We concurrently employed 16S rRNA gene amplicon sequencing to characterize overall microbial community structure by depth in biofilms. Results showed that overall abundances of ARGs were highest in upper layer of biofilm and decreased progressively in lower layers closer to the attachment surface, particularly after the first week of sampling as biofilms matured. Alpha diversity in the biofilms was greatest in the base layers of biofilms, and decreased in upper layers near the fluid-biofilm interface. Alpha diversity also increased progressively over time. Based on beta diversity analyses, overall microbial community structure varied significantly by date of sampling and by depth in the biofilms. These findings are significant because they show that ARGs and genes that can mobilize them throughout wastewater treatment processes are significantly stratified by depth, with higher relative abundances near fluid-biofilm interfaces where horizontal gene transfer may be enhanced and where cells are more likely to detach than in deeper regions of biofilms.

Spatially resolved abundances of antibiotic resistance genes in biofilms for wastewater treatment

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.