Investigating Laccase-Initiated Enzymatic Cascades for Polyolefin Degradation

Sammanfattning

Polyolefins make up the majority of all plastics produced and can be found in a range of applications. Simultaneously, 60% of all plastics are not being recycled, and consequently are accumulating in the environment where it poses serious threats to both the environment, human health, and economies. Current attempts to address the problem have had limited success. An emerging solution is biodegradation - a method that utilizes microorganisms or enzymes for the depolymerization of plastics. In this study, inspired by Oiffer et al., laccase-initiated enzyme cascades were investigated for the degradation of polyethylene and polystyrene (1). More specifically, the laccases PsLAC (Psychrobacter sp. NJ228) and LacA(Bacillus amyloliquefaciens LC02) were investigated as the initial enzyme of the cascade, followed by an alcohol dehydrogenase (LkAdh), a Baeyer Villiger monooxygenase (CHMO), and a commercial cutinase (Hi-cut). All the enzymes, except the commercial cutinase, were expressed recombinantly in E.coli BL21 (DE3). As a pre-treatment, ozonation was tested. HPLC and GC were used to detect any biodegradation. In addition, all recombinant enzymes were characterized using catalytic assays and Differential Scanning Flourimetry. Based on the results, all the enzymes were expressed and purified successfully where PsLAC, LacA, and CHMO showed clear catalytic activities. In contrast, RpKatG and LkADH showed no catalytic activities. Based on FTIR, the pre-treatment using ozonation showed some modifications of polystyrene whereas no chemical modifications were detected on polyethylene. Finally, the laccase-initiated enzyme cascade showed no sign of polyolefin degradation. Due to delays in the measurement of enzyme activity, it is difficult to determine if all enzymes were active during the enzymatic treatment. Thus, more research is needed in order to draw any conclusions whether it was the lack of activity that prevented any degradation or if the enzyme cascade itself was insufficient for polyolefin degradation.