Microbial colonization of microplastics in the Caribbean Sea

Scientific Significance Statement Microplastics, plastic particles smaller than 5 mm that vary in their chemical makeup depending on the plastic type, are emerging marine pollutants that serve as a novel matrix for microbial colonization in the ocean. The communities growing on the microplastics, also termed the plastisphere, may ultimately determine their degradation, deposition, and utilization by the food web, but the factors that shape their composition and development, such as environment, plastic type, and exposure time, are still insufficiently understood. In controlled incubation experiments carried out in a tropical bay in Panama, we show that the composition of a microplastics' bacterial biofilm is not shaped by plastic type or time exposed the environment. On the other hand, we found that the eukaryotic plastisphere was shaped by both plastic type and exposure time and found that specifically diatom communities exhibited preference for some plastic types. Microplastics in the ocean function as an artificial microbial reef, with diverse communities of eukaryotic and bacterial microbiota colonizing its surface. It is not well understood if these communities are specific for the type of microplastic on which they develop. Here, we carried out a 6-week long incubation experiment of six common plastic polymers in Bocas del Toro, Panama. The community composition of prokaryotes based on 16S rRNA gene sequencing data, when judged under a null model analysis, shows that neither plastic polymer type nor time exposed to the environment plays a significant role in shaping biofilm communities. However, the null model analyses of eukaryotic communities based on 18S rRNA gene sequences reveal that they can be significantly influenced by plastic polymer type and time incubated. This was confirmed by scanning electron microscopy, which allowed us to distinguish plastic-specific diatom communities by the end of the incubation period.