Ultrahigh-throughput screening assay for PET-degrading enzymes

In recent years, several PET-degrading enzymes have been identified from both known microorganisms and metagenomic sources in response to the growing environmental issue of polyethylene terephthalate (PET) accumulation. Despite this progress, there is a limited number of (ultra)high-throughput screening methods for assessing PET-hydrolyzing activity without relying on surrogate substrates. This method utilizes the coupled activity of ketoreductases (KREDs) and diaphorase to produce a fluorescent compound (resorufin) in the presence of PET degradation products, offering a more direct and efficient screening approach. A metagenomic KRED was coupled with the diaphorase from Clostridium kluyveri to enable the detection of the hydrolysis of PET degradation products catalyzed by the Bacillus subtilis BS2 esterase. The coupled reaction was established in water-in-oil microdroplets, encapsulating a single E. coli cell per droplet, demonstrating its potential for use in the ultrahigh-throughput screening of metagenomic libraries or randomized libraries for directed evolution campaigns.