Plastic leachates alter the composition of marine microbial communities, not functional potential for plastic degradation.

Plastics in the world's oceans are exposed to diverse environmental stressors that accelerate fragmentation and the leaching of associated additives. The impact of potentially toxic plastic degradation products and additives on marine microorganisms remains poorly understood. We assessed the impact of plastic leachate on marine microbial communities in vitro by exposure to one of four plastic leachates [from linear low-density polyethylene (LLPDE), polyamide-6 (or polycaprolactam; PA6), polyethylene terephthalate (PET), and polylactic acid (PLA)], prepared by immersing plastics in artificial seawater salts broth for three months at 80°C. Microbial communities were then exposed to different leachates. PLA-leachate-exposed communities differed significantly in composition from other plastic-leachate-exposed communities (PERMANOVA, P=0.001) as assessed by 16S rRNA gene and ITS region amplicon sequencing. Communities exposed to PLA leachate contained a higher proportion of Proteobacteria, specifically Halomonas spp. Greater relative abundances of Psathyrellaceae fungi also distinguished PLA-leachate communities. Despite significant differences in the structure of communities exposed to PLA leachate, we found no difference in the relative abundances of differentially expressed gene transcripts associated with known plastic degradation genes. While biodegradable plastics persist for shorter times in the environment than traditional plastics, our study indicates the potential for these plastic types to impact marine microbial communities.