A screening method for polyester films-degrading microorganisms and enzymes

Enzymatic degradation of plastic pollution offers a promising environmentally friendly waste management strategy, however, suitable biocatalysts must be screened and developed. Traditional screening methods using soluble or solubilised polymers do not necessarily identify enzymes that are effective against solid or crystalline polymers. This study presents a simple, time-saving and cost-effective method for identifying microorganisms and enzymes capable of degrading polymeric films. The method was tested on polycaprolactone (PCL), polyethylene terephthalate (PET), polylactate (PLA) and polyhydroxybutyrate/polyhydroxyvalerate (PHB/PHV) films. It involves two steps: first, screening for PCL diol (PCLD)-degrading microorganisms on agar plates, and second, testing these microorganisms on polyester films. Using this screening method, over 100 PCLD-degrading microorganisms and 27 E. coli clones carrying genomic or metagenomic DNA fragments have been isolated. In addition, recombinant cutinases from Streptomyces scabiei and Thermobifida fusca have been tested. Approximately 66 % of the microorganisms forming halos on PCLD agar plates hydrolysed PCL and 6 % - the biaxially oriented PET film. In addition, five PLA- and four PHB/PHV-degrading esterases have been identified. The proposed method is effective for detecting both wild-type and recombinant microorganisms, as well as recombinant enzymes from in vitro transcription-translation reactions. Screening for thermostable and thermophilic enzymes, including those resistant to organic solvents or environmental inhibitors, is also easily implemented.