Carbios proposes standardized enzymatic hydrolysis protocol to advance PET recycling

17 Oct 2023 --- German and French scientists have presented research comparing four high-performance enzymes for PET degradation under industrial conditions, which they say will “pave the way for a standardized enzymatic PET hydrolysis protocol.”

The article “Assessment of Four Engineered PET Degrading Enzymes Considering Large-Scale Industrial Applications” highlights the capabilities of biotechnology company Carbios’ LCCICCG enzyme, which was initially published in Nature Journal in 2020. 

“LCCICCG outperforms the other enzymes, converting 98% of PET into the monomeric products terephthalic acid (TPA) and ethylene glycol (EG) in 24 hours. In addition, we optimized the reaction conditions of LCCICCG toward economic viability, reducing the required amount of enzyme by a factor of three and the reaction temperature from 72 to 68 degrees Celsius,” write the researchers.

“We anticipate our findings to advance enzymatic PET hydrolysis toward a coherent assessment of the enzymes and materialize feasibility at larger reaction scales.”

The findings are published in ACS Catalysis. The researchers anticipate findings of the study to advance materialize feasibility of enzymatic PET hydrolysis at larger reaction scales (Image credit: ACS Catal. 2023).

Propelling enzymatic PET hydrolysis
The study aims to standardize a protocol for enzymatic PET hydrolysis, focusing on conditions relevant to large-scale applications. The study evaluated four engineered PET hydrolases: FAST-PETase, HotPETase, PES-H1L92F/Q94Y and LCCICCG.

FAST-PETase and HotPETase exhibited intrinsic limitations, particularly in terms of their relatively low depolymerization rates, which may hinder their utility on larger reaction scales. 

In contrast, PES-H1L92F/Q94Y and LCCICCG demonstrated higher stability in reactor conditions and achieved near-complete PET conversions (approximately 98%) within 48 and 24 hours, respectively, at specific PET loadings. This makes them strong candidates for enzyme-based PET depolymerization processes on an industrial scale.

However, LCCICCG emerged as the study’s star, surpassing its counterparts by converting 98% of PET into monomeric products, namely TPA and EG, within 24 hours. Furthermore, the research optimized the reaction conditions for LCCICCG, making it more economically viable. 

This optimization reduced the required enzyme quantity by a factor of 3 and lowered the reaction temperature from 72 to 68 degrees Celsius.

The findings from this study are expected to propel enzymatic PET hydrolysis forward, providing a coherent framework for assessing enzyme performance and demonstrating the feasibility of large-scale recycling initiatives.

Industrially biorecycling PET 
Following the research, Carbios has proposed an international standardized method for enzyme comparison.

Carbios and the Toulouse Biotechnology Institute (TBI), France, are now working on a next-generation enzyme — the results of which have not yet been published — slated for use in the “world’s first” PET biorecycling plant, scheduled for commissioning in 2025.

Alain Marty, chief scientific officer at Carbios, says: “With this publication, we wanted to offer the scientific community a standardized method for comparing enzymes under industrial conditions.” 

“This study confirms Carbios’ position as a leader not only for the superior performance of its enzyme for the degradation of PET but in its industrial-scale application for the biorecycling of plastic and textiles.”

Carbios’ pursuit of biological PET recycling has also seen collaborations with enzymologists, professor Uwe Bornscheuer from the University of Greifswald, Germany, and professor Gert Weber from Helmholtz-Zentrum Berlin.

ACS assessment 
The study authors assert that in recent years, enzymatic recycling has emerged as a complementary solution to traditional thermomechanical methods for recycling PET, especially when dealing with colored, opaque and mixed PET materials. 

Numerous promising hydrolases capable of depolymerizing PET have been identified and improved through global efforts in protein engineering. However, the scientists flag that a major challenge has been the lack of uniformity in experimental protocols, making it challenging to compare enzyme performance and its suitability for large-scale applications.

“In the past few years, numerous publications dealing with the discovery and engineering of PET hydrolases have been released. To improve the activity and thermostability of such PETases (hydrolase enzyme catalyzing PET), various concepts of protein engineering were implemented, such as rational design, directed evolution or AI-assisted in silico protein design,” the researchers discuss.

“The field has greatly benefited from these studies since they have opened a plethora of new possible avenues for enzymatic PET recycling. Unfortunately, a thorough comparison of enzyme performance remains problematic since no international scientific consensus for evaluating PET hydrolase performance has emerged.”

Edited by Radhika Sikaria