Cold-water gut isolate from threespine stickleback ( Gasterosteus aculeatus ) reveals polypropylene surface oxidation and co-culture inhibition

ABSTRACT Polyethylene terephthalate (PET) and polypropylene (PP), two of the most widely produced plastics in the United States, persist in diverse environments worldwide and may persist longer in cold-water environments where plastic-degrading microbial taxa have been poorly characterized. Understanding how gut microbes interact and contribute to plastic degradation is essential for developing potential microbiome-based bioremediation strategies. We isolated 184 microbes from wild Alaskan threespine stickleback ( Gasterosteus aculeatus ) guts across six bodies of water and screened them for their plastic-degrading potential using lipase/esterase assays and biofilm formation on PET and PP. We discovered that while some members of the stickleback gut microbiota have high lipase, esterase, and biofilm activity, that activity is enhanced or suppressed by other microbes. Isolates with the highest plastic-degrading potential were incubated in minimal media with PET or PP as the primary carbon source to determine whether plastic degradation occurs. While no detectable changes were observed on PET, surface analysis identified a Pseudomonas trivialis strain that exhibited evidence of PP surface oxidation in monoculture; however, this activity was suppressed in the presence of another gut isolate, Pseudomonas germanica . These results demonstrate that microbes associated with the gut microbiome of a cold-water fish possess plastic-degrading potential and provide insights into how microbial interactions can inhibit bioremediation of plastic pollution in cold-water environments. IMPORTANCE Plastic pollution persists in cold, freshwater environments and presents a significant challenge to the ecosystem, where low temperatures slow abiotic degradation, and microbial contributions remain poorly understood and understudied. Here, we isolated 184 microbes from adult Alaskan threespine stickleback guts across six bodies of water and screened for plastic-degradation potential using plate-based assays under both monoculture and co-culture conditions. We identified a stickleback gut-associated microbe that can oxidize polypropylene and identified a second microbe, isolated from the same environment, that can significantly suppress polymer oxidation when in co-culture. Together, these findings demonstrate that microbial interactions influence plastic-degradation abilities and support efforts to identify ecologically relevant microbes or enzymes for bioremediation efforts.