Characterization of novel fungal-algal symbiosis on LDPE plastic surfaces in the Mediterranean Sea

Abstract Plastic debris in the ocean serves as a stable ground for the formation of a complex ecosystem, termed plastisphere, which includes a variety of organisms from different taxonomic groups. Not much is known about the relationships between the organisms of the plastisphere communities. In this study we describe a novel symbiotic relationship between a marine fungus and several species of diatoms on plastic surfaces that were submerged in the water of a Mediterranean Sea marina in Israel. Scanning electron microscope images of the surfaces revealed a network of fungal hyphae with multiple diatom cells attached to them via the side or the tip of their body. Using DNA metabarcoding for the fungal Internal Transcribed Spacer (ITS) barcode locus, we found that the symbiotic fungus belongs to the phylum Ascomycota, and that it is more abundant on low density polyethylene (LDPE) surfaces compared to other plastic polymers and glass. We hypothesize that the observed symbiotic relationship may have mutual benefits for both parties, including surface-anchoring for the diatoms and nutritional benefits for the fungus, that reflects a recent adaptation for life on floating plastic debris.