Novel PET hydrolases derived from thermophilic microorganisms

Millions of tons of plastic waste are generated every year due to the nature of their constituting polymers, which do not biodegrade or absorb into the environment. Consequently, the increase in plastic waste has become a pressing environmental issue. Moreover, during their use, plastics may break down forming small fragments or particles with a diameter less than 5 mm, named microplastics. These latter constitute an emerging environmental and human health concern. Indeed they have been found everywhere on earth, from the bottom of the oceans to polar regions Toxicological studies reported that the exposure to microplastics induces severe toxic effects, involving oxidative stress, metabolic disorder, immune response, as well as neurotoxicity. In recent years, biodegradation has emerged as a new green technology for upcycling plastic waste. This process relies on the action of enzymes produced by microorganisms, which are able to break down plastic materials into their basic components, making them easy to recycle. In 2016, it has been reported that a bacterial strain called Ideonella sakaiensis 201-F6 was identified exhibiting the ability to produce two enzymes, polyethylene terephthalate hydrolase (PETase) and mono (2-hydroxyethyl) terephthalic acid hydrolase (MHETase). These enzymes enable Ideonella sakaiensis to use PET as their sole carbon source. Since then, extensive research has been carried out to identify other bacterial strains capable of producing enzymes catalyzing plastics degradation. In this context, the identification of new bacterial hydrolases deriving from thermophilic microorganisms can give new insight into plastic biodegradation in harsh conditions, such as high temperatures. Through meta-genomic approaches, a novel thermophilic PET hydrolase, denominated PP PETase (PP), has been recently identified from geothermal samples. This novel enzyme was produced in recombinant form and purified to carry on it physico-chemical analyses and assess the thermal stability and structural features of PP in order to provide deeper insights into its functional and structural properties and identify its potential application.