Strategies for Improving the Bacterial Biodegradation of PET

Plastic waste and its persistent presence in the environment pose significant global challenges. Among various types of plastics, synthetic ones like polyethylene terephthalate (PET) are mostly used for packaging and has comprised a major part of plastic waste. PET is particularly resistant to degradation, mainly due to its high content of aromatic terephthalate units. While biodegradation is an environmentally friendly method for tackling this waste, it is proven to be somewhat inefficient. One contributing factor is that the temperature required for bacterial growth is significantly lower than the glass transition temperature of PET.

To circumvent this limitation, various complementary techniques have been proposed in this project to enhance biodegradation of PET using Ideonella sakaiensis (I. sakaiensis) and Pseudomonas mendocina (P. mendocina). These methods encompass physical approaches (e.g., UV radiation), chemical treatments (e.g., alkaline treatment), biochemical strategies (utilizing surfactants like cationic surfactant dodecyl trimethylammonium bromide (DTAB) and non-ionic surfactant Dodecyl polyethylene oxide-23 ether (Brij-35)), as well as enzymatic treatment using Fusarium culmorum supernatant (FSC) which contains cutinase. Furthermore, the impact of the quorum sensing molecule (QSM) (specifically, 3-oxo-C12-HSL) on PET degradation was investigated in the context of DTAB-treated, FSC-treated, and DTAB-FSC-treated PET up to eight weeks in the presence of the mentioned bacteria with particular emphasis on I. sakaiensis for its better performance compared to P. mendocina under the chosen process conditions.

A range of analytical techniques, including Fourier Transform Infra-Red spectroscopy (FTIR), biofilm assays, high-pressure liquid chromatography (HPLC), high-resolution microscopy, and scanning electron microscopy (SEM), were employed to evaluate the outcomes of these treatments on PET and its biodegradation potential.

Notably, FSC treatment, in conjunction with the presence of the I. sakaiensis bacterial culture supplemented with QSM in Yeast Extract-Sodium Carbonate and Vitamins (YSV) medium, exhibited significant promise for enhancing PET degradation within one week.

FTIR spectroscopic analyses were employed to probe structural alterations within the PET polymer. The FTIR findings demonstrated the substantial progress achieved, unveiling an impressive ~89.0% transmittance rate post FSC treatment of PET followed by one week of incubation using the I. sakaiensis culture supplemented by QSM. This enhanced transmittance reflects notable modification in PET molecular bonds, signifying successful polymer breakdown.

Furthermore, assessments of microstructural transformations were carried out through high-resolution microscopy and Scanning Electron Microscopy (SEM). These observations concurred with the FTIR results, visually attesting to the efficacy of FSC treatment in the I. sakaiensis culture supplemented by QSM. The surfaces of FSC-treated PET exhibited notable roughness compared to untreated PET, coupled with an increased surface porosity. These structural modifications validate the findings derived from FTIR spectroscopy, fortifying the substantial strides made in PET biodegradation.