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

Current knowledge about the microbial communities inhabiting the stormwater quality improvement devices (SQIDs) for road runoff is scarce. However, as a bioactive compound of these systems, microbes can facilitate water quality improvement through the biodegradation or precipitation of dissolved contaminants. On the other hand, these contaminants may select for stress resistant opportunistic microbial strains, which are discharged into surface waters or groundwater.

In this study, the microbial community of two SQIDs with different design 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 both by seasonality and by the SQID design.

The heavy metal content of the SQIDs was correlated to intl1 and distinct microbial groups. The filter media led to an enrichment and subsequent discharge of Intl1 gene cassettes 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 of the SQIDs, and subsequently influence the microbial community and the genes released with the treated water.