Industrial WWTP Sludge as a Reservoir of Putative Plastic-Degrading Enzymes: Insights Into Microbial Community Structure.

Plastic pollution has emerged as a major environmental challenge. While various microorganisms and enzymatic mechanisms involved in plastic degradation have been described, the microbial communities present in wastewater treatment plants (WWTPs) - particularly those linked to the oil industry - remain largely underexplored as potential reservoirs of plastic-associated metabolic functions. This study evaluated the potential of microbial communities from an industrial WWTP located in an oil refinery complex to colonise different plastic polymers, as well as their genetic potential for plastic-associated transformations. Industrial sewage sludge was incubated with four polymeric substrates: low-density polyethylene, polyamide, polypropylene, and polystyrene. Metagenomic analysis of the inoculum was performed to assess its potential to harbour genes encoding proteins with sequence similarity to enzymes previously associated with plastic transformation or degradation. Additionally, 16S rRNA amplicon sequencing studied changes in microbial community composition during biofilm formation. Proteobacteria accounted for approximately 50% of the microbial relative abundance in the inoculum. Metagenomic screening identified 773 genes encoding proteins with homology to enzymes previously associated with plastic degradation. Biofilms developed on plastic surfaces were dominated by Proteobacteria and Bacteroidota, although differences in dominant classes and orders were observed depending on the polymer type. Correlation analyses further indicated associations between specific microbial taxa and individual plastic types. Overall, the results highlight industrial WWTP sludge as a potential reservoir of microorganisms associated with plastic colonisation, providing new insights into plastisphere community assembly in engineered environments.