Plastic fragments drifting near coastlines host communities of microorganisms that differ from those living freely in seawater.
A surface submerged in the ocean does not remain sterile for long. Microscopic organisms attach themselves to it and gradually form a community. Plastic waste thus provides new, lasting surfaces. This habitat formed around plastic is called the “plastisphere.”
This time, the researchers focused on archaea. These microscopic organisms look like bacteria on the outside, but belong to another major branch of life. They are present in many environments, including the oceans, and some participate in the natural transformations of carbon, nitrogen, or sulfur.
To determine the impact of plastic, the team compared debris collected from coastal marine environments with the surrounding water. The researchers analyzed the genetic material present in the samples. This method makes it possible to identify groups of archaea and estimate the biological functions associated with their genes.
The communities established on the plastic showed greater diversity and varied more from one sample to another. Some major groups of archaea were also more strongly represented there than in the surrounding water. Plastic therefore serves not only as a neutral surface: it selects a particular community.
The differences also concern what these organisms can do. The researchers found more genes associated with transformations of methane, nitrogen, and sulfur on the plastics.
Another observation was that the gap between the communities on the plastic and those in the water increased when pressure from human-derived chemical substances was stronger. This indicates that several forms of pollution can act together on coastal microbial communities, although the study does not yet make it possible to measure all their consequences.
The study therefore establishes that archaea also respond to this new habitat. Until now, they had received less attention than bacteria in research devoted to the plastisphere.
The authors now want to better determine how these changes are actually reflected in carbon, nitrogen, and sulfur exchanges. Measuring the activity of the organisms, rather than just their genes, will make it possible to estimate the concrete effect of these artificial habitats on coastal areas.