Plastic Bag at Sea Is a Heaven for Diatoms: Species Diversity and Composition Analysis of Marine Eukaryotic Communities on Polyethylene

Polyethylene is a very common plastic polymer that has many uses in our life. Its low-density form is commonly used to produce disposable plastic bags in massive quantities around the globe. Most bags are trashed and many reach the ocean, become a major plastic pollutant and contribute to the ocean microplastic pool. Since polyethylene degradation rate is slow, it serves as a good substrate for colonialization of a variety of microorganisms. While some studies characterized the prokaryotic biota on marine plastic litter, very little is known about the microbial eukaryotic communities. In this study we aimed to characterize the structure and the composition of the eukaryotic biota on polyethylene bags in the Mediterranean Sea. Plastic bags were placed at the Herzeliya marina, Israel and in open water at a proximal location. After one month at sea eDNA was extracted from the bags and the from the water. Genetic markers including 18S and COI were amplified, followed by MinION nanopore high-throughput sequencing. A bioinformatic pipeline was developed to identify eukaryotic taxa based on comparison to the Silva and NCBI databases. Our sequencing results reveal highly diverse repertoires of plastic-lover protists which consisted primarily of marine diatoms most of which were not abundant or were not found in the water column. Scanning electron microscopy was performed on fixed samples confirming the molecular identification of taxa and revealed complex relationships between diatoms, bacteria and other eukaryotes. We consider this study as a ground for further, more comprehensive research in this unexplored new field.