Microbial retention and resistances in stormwater quality improvement devices treating road runoff

In this study, the microbial community of two types of SQIDs were analyzed to determine the microbial load, retention, composition, and mobile resistance genes in the filter media and the microbial composition in the treated runoff. The bacterial abundance of the SQIDs was relatively stable over time in effluent water samples. Although the microbes were replaced by new taxa in the effluent there was no major retention of cells or microbial genera. The communities were influenced by seasonality and by the SQID design. The heavy metal retention by the SQIDs was correlated to intl1 and distinct microbial groups. The filters partly led to an enrichment and subsequent discharge of Intl1 gene cassettes (partly exceeding the cell number proxy 16S) carrying several heavy metal and multidrug resistance genes (e.g. czrA, czcA, silP, mexW and mexI). Overall, the results suggest that different engineering designs affect the bacterial communities growing on the filter media of the SQIDs, and subsequently influence the microbial community and the genes released with the treated water.