Turns out life in the gutter is not all bad. Scientists have just discovered that gutters lining the streets of Paris are teeming with microscopic life that may help improve water quality of urban storm water runoff.

The research team, comprised of biologists from the BOREA Biology of Aquatic Organisms and Ecosystems research unit in France and a fellow scientist from the Max Planck Institute for Terrestrial Microbiology in Germany, have found that gutters running alongside Parisian streets provide an oasis for a myriad of microscopic organisms, including fungi, microalgae and sponges, as well as mollusks. These urban aquatic communities may provide beneficial ecological services, for example helping to clean storm water and reducing urban waste by breaking down solid organic matter as well as urban contaminants such as engine oil and vehicle exhaust fumes that could otherwise degrade water quality. Gaining a clearer understanding of what organisms make up these communities, and the ecological niche they fill, can help us better understand the ecological services that gutter ecosystems render.

A storm water drain in Paris

The results of the study, which is the first to shed light on the complex biodiversity of microorganisms living on the streets of Paris, appeared in the October 2017 edition of the ISME Journal. After noticing the characteristic brown and green tinge of the water flowing in Paris city gutters, as well as bubbles — which are a tell-tale sign of photosynthesis taking place, BOREA researchers suspected that there may be microalgae present in the water. So they set about analyzing non-potable water samples they collected from various locations to identify what microorganisms were present. Sample sites included street gutters, water outlets located on street curbs that pump water from either the Seine or the Canal de l'Ourcq which is used for street cleaning, as well as water collected directly from the Canal de l'Ourcq and the Seine.

They identified a remarkable 6,900 possible species of eukaryote microorganisms in the roughly one hundred water and biofilm samples they collected off the streets of Paris. Unicellular diatoms were the most abundant, but other unicellular eukaryotes (organisms with a nucleus and organelles) such as amoebas, Rhizaria and alveolates; fungi (including species that are recognized as decomposers); sponges; and even mollusk species were observed.

More surprising, the researchers around 70% of the species detected in gutter water were not present in the non-potable source water. The composition of the microorganism communities varied greatly between the sites sampled, which according to the researchers, suggests they may originate as a result of human activity or that they have adapted to thrive in the specific urban location where they are found. The researchers conclude that gutters on city streets and the microorganisms they support seem to represent a unique ecosystem that may have a specific, but as yet undiscovered, ecological role to fulfill.

Clearly intrigued, the scientists stress that we need to know more about these microorganisms: What exactly are they? What function do they serve? Do they play a key role as minute curbside treatment plants, helping to clean wastewater? How have they adapted to life on the city streets? Should we be monitoring them more closely? To answer these questions, the researchers hope to expand this study by looking at other forms of life, such as bacteria, over a longer timeframe, and assessing microscopic life in gutter water of other cities too.