Microorganisms play crucial roles in all biogeochemical processes, and shifting microbial communities have potential implications for the marine ecosystem. Therefore, the impact of the ubiquitous plastic pollution on composition and function of marine microbial communities represents a highly relevant research topic from an ecological, environmental, and microbiological perspective. Previous studies revealed that plastics in the oceans are colonized by diverse pro- and eukaryotic communities, but many open questions, in particular on functional level, remain. This session will focus on microplastic microbiomes from different parts of the world, their metabolic profiles, and how spatial and seasonal factors play a role in shaping these plastic biofilms. We will further look into topics highly discussed in this field of research, namely whether microplastics carry potential harmful microorganisms and traits, and whether marine microorganisms can contribute to biodegradation of plastics. Overall, we aim at a better understanding of the effect plastic pollution can have on microbial ecology and ecosystem functioning.