The assembly and ecological roles of biofilms attached to plastic debris of Ashmore reef

Plastic pollution in the ocean is a global environmental hazard aggravated by poor management of plastic waste and growth of annual plastic consumption. Microbial communities colonizing the plastic's surface, the plastisphere, has gained global interest resulting in numerous efforts to characterize the plastisphere. However, there are insufficient studies deciphering the underlying metabolic processes governing the function of the plastisphere and the plastic they reside upon. Here, we collected plastic and seawater samples from Ashmore Reef in Australia to examine the planktonic microbes and plastic associated biofilm (PAB) to investigate the ecological impact, pathogenic potential, and plastic degradation capabilities of PAB in Ashmore Reef, as well as the role and impact of bacteriophages on PAB. Using high-throughput metagenomic sequencing, we demonstrated distinct microbial communities between seawater and PAB. Similar numbers of pathogenic bacteria were found in both sample types, yet plastic and seawater select for different pathogen populations. Virulence Factor analysis further illustrated stronger pathogenic potential in PAB, highlighting the pathogenicity of environmental PAB. Furthermore, functional analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways revealed xenobiotic degradation and fatty acid degradation to be enriched in PABs. In addition, construction of metagenome-assembled genomes (MAG) and functional analysis further demonstrated the presence of a complete Polyethylene (PE) degradation pathway in multiple Proteobacteria MAGs, especially in Rhodobacteriaceae sp. Additionally, we identified viral population presence in PAB, revealing the key role of bacteriophages in shaping these communities within the PAB. Our result provides a comprehensive overview of the various ecological processes shaping microbial community on marine plastic debris.