New insights into the functioning and structure of the PE and PP plastispheres from the Mediterranean Sea

Plastic debris are accumulating in the marine environment and aggregate microorganisms that form a new
ecosystem called the plastisphere. Better understanding the plastisphere is crucial as it has self-sufficient organization
and carries pathogens or organisms that may be involved in the pollutant adsorption and/or plastic
degradation. To date, the plastisphere is mainly described at the taxonomic level and the functioning of its
microbial communities still remains poorly documented. In this work, metagenomic and metaproteomic analyzes
were performed on the plastisphere of polypropylene and polyethylene plastic debris sampled on a pebble beach
from the Mediterranean Sea. Our results confirmed that the plastisphere was organized as self-sufficient ecosystems
containing highly active primary producers, heterotrophs and predators such as nematode. Interestingly,
the chemical composition of the polymer did not impact the structure of the microbial communities but rather
influenced the functions expressed. Despite the fact that the presence of hydrocarbon-degrading bacteria was
observed in the metagenomes, polymer degradation metabolisms were not detected at the protein level. Finally,
hydrocarbon degrader (i.e., Alcanivorax) and pathogenic bacteria (i.e., Vibrionaceae) were observed in the plastispheres
but were not very active as no proteins involved in polymer degradation or pathogeny were detected.
This work brings new insights into the functioning of the microbial plastisphere developed on plastic marine
debris.