The unexpected habitat in sewer pipes for the propagation of microbial communities and their imprint on urban waters

• Arcobacter, Acinetobacter, and Aeromonas dominate communities in sewage. • Pipe organisms in sewage influent have abundance patterns distinct from biofilm. • The highstress environment selects for organisms with unique fitness strategies. • Urban sewer pipes leak and during rain, sewage is mobilized to stormwater systems. • Arcobacter is an indicator of urban impact and readily detected in waters worldwide. Modern urban sewer pipe infrastructure is a unique niche where microbes can thrive. Arcobacter , Acinetobacter , Aeromonas , and Trichococcus are among the organisms that dominate the microbial community of sewage influent, but are not major members of human fecal microbiome, drinking water, or groundwater. Pipe resident communities in untreated sewage are distinct from sewer biofilm communities. Because of their high biomass, these organisms likely have a role in biotransformation of waste during conveyance and could represent an important inoculum for treatment plants. Studies demonstrate stormwater systems act as direct conduits for sewage to surface waters, releasing organisms propagated in sewer pipes. Frequent occurrence of these pipe residents, in particular Arcobacter , demonstrates the extent that urban infrastructure impacts rivers, lakes, and urban coasts worldwide.