*Review* **Microbial Genes for a Circular and Sustainable Bio-PET Economy**

#### **Manuel Salvador 1, Umar Abdulmutalib 1, Jaime Gonzalez 1, Juhyun Kim 1, Alex A. Smith 1, Jean-Loup Faulon 2,3,4, Ren Wei 5, Wolfgang Zimmermann 5 and Jose I. Jimenez 1,\***


Received: 23 April 2019; Accepted: 13 May 2019; Published: 16 May 2019

**Abstract:** Plastics have become an important environmental concern due to their durability and resistance to degradation. Out of all plastic materials, polyesters such as polyethylene terephthalate (PET) are amenable to biological degradation due to the action of microbial polyester hydrolases. The hydrolysis products obtained from PET can thereby be used for the synthesis of novel PET as well as become a potential carbon source for microorganisms. In addition, microorganisms and biomass can be used for the synthesis of the constituent monomers of PET from renewable sources. The combination of both biodegradation and biosynthesis would enable a completely circular bio-PET economy beyond the conventional recycling processes. Circular strategies like this could contribute to significantly decreasing the environmental impact of our dependence on this polymer. Here we review the efforts made towards turning PET into a viable feedstock for microbial transformations. We highlight current bottlenecks in degradation of the polymer and metabolism of the monomers, and we showcase fully biological or semisynthetic processes leading to the synthesis of PET from sustainable substrates.

**Keywords:** plastics; biodegradation; sustainability; upcycling; biotransformations; polyethylene terephthalate; terephthalate; ethylene glycol
