Diversity and distribution of potential polyethylene terephthalate and polypropylene plastic-degrading bacteria communities in deep-sea cold-seep ecosystems.

Biodegradation represents a promising strategy for the remediation of marine plastic pollution. Notably, deep-sea cold-seep ecosystems nurture exceptionally abundant microbial hydrocarbon-degrading bacterial resources. Due to structural similarities between plastics and natural hydrocarbons in cold seeps, cold-seep microorganisms may possess potential enzymatic strategies suited to plastic breakdown. Therefore, this study combined 1 year in situ inoculation and 168 days of laboratory enrichment experiments to investigate the diversity and distribution characteristics of cold-seep bacteria that respond to polyethylene terephthalate (PET) and polypropylene (PP) degradation. Enriched communities were able to grow utilizing plastics as a sole carbon source, and distinct grooves and cracks were observed on plastic films following enrichment. During cultivation, taxa that appeared unable to utilize plastics declined in abundance, while putative plastic-degrading taxa became enriched. Amplicon sequence variant (ASV) abundance dynamics revealed 24 candidate PET-degrading and 22 candidate PP-degrading ASVs, which exhibited an expanded spectrum of plastic degradation capabilities compared with literature reports. Furthermore, these putative degraders were widespread in natural cold seeps, and nutrient-rich sites appeared more conducive to the enrichment of plastic degraders. This work broadens the understanding of the plastic-degrading potential of cold-seep ecosystems and identifies candidate taxa for further biochemical and biodegradation characterization. Plastic pollution is accumulating in the ocean, including the deep sea, where removal is extremely difficult, and natural breakdown is poorly understood. This study explores whether microorganisms from deep-sea cold-seep ecosystems can help degrade common plastics such as polyethylene terephthalate and polypropylene. Cold seeps naturally contain methane and petroleum-like hydrocarbons, so their microbes may already have biological tools for breaking down plastic-like compounds. By combining year-long deep-sea exposure with laboratory enrichment, this work identified bacterial groups that increased in abundance when plastics were the only available carbon source and observed visible damage on plastic surfaces. These findings suggest that cold seeps may act as natural reservoirs of previously overlooked plastic-degrading microbes. The study expands our understanding of how plastics may persist or break down in deep marine environments and provides candidate bacteria for future biodegradation research.