Polymer Matters: Substrate-Specific Plastic Biofilms in Glacial Melt Host Bacteria Linked to Polymer Degradation

Biofilms dominate microbial life in the cryosphere, drive the geochemical cycles and support glacier-fed food webs. The cryosphere covers 10% of Earth’s land and is primarily fed by deposition, also one of the main drivers of microplastics (<5 mm) entering remote alpine ecosystems. However, microbial colonization of plastics in the cryosphere remains poorly understood. We conducted an in situ incubation experiment in a proglacial lake to expose polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and glass substrates (non-polymer control) over 10 weeks, covering the ablation phase. After 4, 6, 8, and 10 weeks, we sampled each substrate, along with lake water as non-surface control and water parameter analysis. Long-read 16S rRNA nanopore sequencing revealed substrate-specific biofilms on polymers, distinct from the non-polymer control and non-surface control after one month. The community structure was significantly shaped by dissolved organic carbon, dissolved phosphorus, time, and material type. Of all detected taxa, 1.4% matched known polymer degraders, with 73.4% enriched on PE surfaces, primarily within the first 6 weeks. Also, the polymer type shaped microbial succession, with PE being similar to PP and PET with glass. These findings highlight plastic as an emerging microbial habitat with the potential to alter sensitive high-alpine ecosystems.