BackgroundThe biological degradation of plastics is a promising method to counter the increasing pollution of our planet with artificial polymers and to develop eco-friendly recycling strategies. Polyethylene terephthalate (PET) is a thermoplast industrially produced from fossil feedstocks since the 1940s, nowadays prevalently used in bottle packaging and textiles. Although established industrial processes for PET recycling exist, large amounts of PET still end up in the environment—a significant portion thereof in the world’s oceans. In 2016, Ideonella sakaiensis, a bacterium possessing the ability to degrade PET and use the degradation products as a sole carbon source for growth, was isolated. I. sakaiensis expresses a key enzyme responsible for the breakdown of PET into monomers: PETase. This hydrolase might possess huge potential for the development of biological PET degradation and recycling processes as well as bioremediation approaches of environmental plastic waste.ResultsUsing the photosynthetic microalga Phaeodactylum tricornutum as a chassis we generated a microbial cell factory capable of producing and secreting an engineered version of PETase into the surrounding culture medium. Initial degradation experiments using culture supernatant at 30 °C showed that PETase possessed activity against PET and the copolymer polyethylene terephthalate glycol (PETG) with an approximately 80-fold higher turnover of low crystallinity PETG compared to bottle PET. Moreover, we show that diatom produced PETase was active against industrially shredded PET in a saltwater-based environment even at mesophilic temperatures (21 °C). The products resulting from the degradation of the PET substrate were mainly terephthalic acid (TPA) and mono(2-hydroxyethyl) terephthalic acid (MHET) estimated to be formed in the micromolar range under the selected reaction conditions.ConclusionWe provide a promising and eco-friendly solution for biological decomposition of PET waste in a saltwater-based environment by using a eukaryotic microalga instead of a bacterium as a model system. Our results show that via synthetic biology the diatom P. tricornutum indeed could be converted into a valuable chassis for biological PET degradation. Overall, this proof of principle study demonstrates the potential of the diatom system for future biotechnological applications in biological PET degradation especially for bioremediation approaches of PET polluted seawater.

The author’s middle name is missed out in the original publication of the article [1]. The correct coauthor’s name is Tobias J. Erb.

In this study, we investigated an SBP (DctP ) of a tripartite ATP-independent periplasmic transport system (TRAP) in Advenella mimigardefordensis strain DPN7 . Deletion of dctP as well as of the two transmembrane compounds of the tripartite transporter, dctQ and dctM, impaired growth of A. mimigardefordensis strain DPN7 , if cultivated on mineral salt medium supplemented with d-glucose, d-galactose, l-arabinose, d-fucose, d-xylose or d-gluconic acid, respectively. The wild type phenotype was restored during complementation studies of A. mimigardefordensis ΔdctP using the broad host vector pBBR1MCS-5::dctP . Furthermore, an uptake assay with radiolabeled [ C(U)]-d-glucose clearly showed that the deletion of dctP , dctQ and dctM, respectively, disabled the uptake of this aldoses in cells of either mutant strain. Determination of K performing thermal shift assays showed a shift in the melting temperature of DctP in the presence of d-gluconic acid (K 11.76 ± 1.3 µM) and the corresponding aldonic acids to the above-mentioned carbohydrates d-galactonate (K 10.72 ± 1.4 µM), d-fuconic acid (K 13.50 ± 1.6 µM) and d-xylonic acid (K 8.44 ± 1.0 µM). The sugar (glucose) dehydrogenase activity (E.C.1.1.5.2) in the membrane fraction was shown for all relevant sugars, proving oxidation of the molecules in the periplasm, prior to transport.