HUMAN, ANIMAL, OR INFRASTRUCTURE: IDENTIFYING SOURCES OF URBAN-DERIVED BACTERIA TO AQUATIC ENVIRONMENTS

Freshwater resources throughout the Great Lakes region receive stormwater runoff from heavily urbanized areas. While fecal indicator bacteria contained in this runoff are typically the focus of microbiological investigations, non-fecal bacterial loads from aerosols, soil, pipes, and other sources are also transported to rivers, streams, estuaries and lakes. A multi-year investigation of stormwater in the Milwaukee metropolitan area revealed evidence of both sporadic and chronic fecal pollution in many outfalls across diverse watersheds. While some sites were impacted by human fecal pollution, the majority of fecal contamination appeared to be of non-human origin. High-throughput amplicon sequencing of bacterial 16S rRNA genes provided characterization of both “clean” and impacted stormwater microbial communities. The composition of urban stormwater bacterial communities was highly diverse both within and among samples; variability resulted from differences in the watershed drained, storm intensity, pollutant contributions, as well as other undetermined factors. Sequences from the fecal families Ruminococcaceae and Lachnospiraceae were analyzed in detail to better differentiate human and animal pollution sources and allowed us to estimate the relative contribution from urban wildlife to the stormwater fecal signature. We also identified members of the non-fecal urban microbial community using a statistical biomarker discovery tool to identify the bacteria that were most strongly associated with stormwater infrastructure. The dominant bacteria in the non-fecal urban signature were pipe-associated organisms that included strains from the genera Acinetobacter, Aeromonas, and Pseudomonas. These infrastructure-associated bacteria made up the majority of the urban flux from stormwater outfalls to adjacent aquatic environments, where they are present in maximum relative abundance during or immediately after storm event, but maintain a significant persistent presence even during baseflow conditions.