Astonishingly Abundant and Unsuspected Life Found in City Gutters

Diatoms and gutters in the streets of Paris.

© Pascal Jean Lopez / Laboratory of Biology of Aquatic Organisms and Ecosystems (CNRS / MNHN / IRD / UPMC / University of Caen / University of the West Indies).

Scientists from the BOREA Biology of Aquatic Organisms and Ecosystems research unit (CNRS / MNHN / IRD / UPMC / University of Caen / Université des Antilles)–together with a colleague from the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany– conducted the research.

Published in the ISME Journal on October 13, 2017, the researchers’ findings are the first to reveal the unsuspected biodiversity of microscopic life in Paris city streets.

Scientists from the BOREA research unit first suspected the presence of microalgae in Paris streets after noting the characteristic green or brown color of gutter water and observing the presence of bubbles, which are the result of photosynthetic activity. The researchers analyzed different samples of non-potable water from the Seine, the Ourcq Canal, curbside water outlets (for street cleaning), and street gutters to identify the microorganisms they harbored.[2]

The team identified 6,900 potential species[3] of eukaryotes[4] in the hundred or so samples of water and biofilms (consisting of communities of microorganisms) collected from every district of Paris. Diatomaceous microalgae make up a large part of this biodiversity. Also identified were other unicellular eukaryotes (i.e., amoebas, alveolates, and Rhizaria), fungi (including some known decomposers), sponges, and mollusks. 

Even more astonishingly, analyses revealed that nearly 70% of these species were not found in the non-potable water sources. The profiles of these microbiological communities vary greatly between sampling sites, suggesting their origin may be associated with human activities or that the microorganisms have adapted to their specific urban environment.

Hence, street gutters and the microscopic life they host appear to constitute a unique ecosystem with ecological roles still to be discovered. What are these microorganisms exactly? What do they do? Do they help clean wastewater, like tiny roadside treatment plants? How did they adapt to city life? Should they be monitored? These are all questions the researchers hope to answer by studying other kinds of life–such as prokaryotes, organisms devoid of cell nuclei, like bacteria –over longer periods of time, and even in different cities.

Notes:

1 This study was launched as part of a FSPP program (Exploratory Projects First Support) of the CNRS.

2 In Paris, non-potable water, dedicated to street cleaning, for example, is collected via three pumping stations (two in the Seine and one in the Canal de l’Ourcq) and stored in 7 tanks before being distributed in the gutter network.

3 These microorganisms are classified in OTU, an operational taxonomic unit, which groups together phylogenetically close individuals.

4 Eucaryotes are organisms, unicellular or multicellular, having a nucleus and organelles, unlike bacteria and archaea.