The PLASTISEA consortium, funded by the German Federal Ministry of Education and Research (BMBF, grant 161B0867F), ran from 1 February 2020 to 31 August 2023. The University of Kiel (CAU) contributed mainly to work packages AP 1 and AP 2 and partially to AP 6. Partners included the University of Hamburg (UHH), the German Research Centre for Marine Biology and Ecology (GEOMAR), the Alfred Wegener Institute (AWI) and other research institutions. The project’s aim was to discover and develop marine enzymes and microorganisms capable of degrading synthetic polymers such as PET, PU, PE and PA, thereby addressing the growing problem of micro‑ and nanoplastic pollution in oceans.

In AP 1, CAU performed an extensive in‑silico search for novel PET‑degrading enzymes (PETases) and polyurethane‑degrading enzymes (PURases) within archaeal genomes. Using a Hidden Markov Model (HMM) derived from known PETases, the archaeal section of the NCBI database yielded more than 500 candidate sequences. Phylogenetic filtering and 3D modelling on the Robetta server narrowed this set to eight promising PETase candidates (PET45–PET52) that were synthesized in the pET21a(+) expression vector and characterized in collaboration with UHH. A parallel search in the university’s archaeal strain collection identified 16 isolates; eight of these harboured putative PETase genes (KAP1–KAP8). Structural comparison with the bacterial IsPETase from Ideonella sakaiensis revealed that KAP2, KAP7 and KAP8 possess the conserved catalytic triad Asp‑His‑Ser and key residues for PET binding, while their lid domains are smaller than those of known PETases, suggesting potentially higher activity. The genes were amplified by PCR, cloned, expressed, purified and subjected to functional assays, although detailed activity data are pending.

For PURases, the archaeal HMM search returned over 1,000 candidates, mainly annotated as amidases. This list was reduced to roughly 50 sequences with >50 % identity to known PURases; these remain to be cloned and tested. GEOMAR supplied approximately 3,000 metagenome‑assembled genomes (MAGs) from Atlantic, Pacific and TARA ocean samples. CAU identified 8,725,954 genes, of which 8,637,875 were protein‑coding. Screening these with the PETase and PURase HMMs uncovered 64 putative PETases, 7,529 PUR amidases and 96 PUR esterases with bitscores above 100. These sequences were forwarded to GEOMAR for experimental validation.

AP 2 focused on building a functional enzyme toolbox. CAU expressed and purified the selected archaeal PETases and PURases, and performed kinetic characterisation. In parallel, enrichment cultures from Kiel Fjord, the Elbe River and plastic debris collected by GEOMAR were established. Alcanivorax isolates were observed adhering to various polymers by confocal microscopy and scanning electron microscopy, revealing pili structures that likely mediate surface attachment. Long‑term incubations of Aurelia aurita polyps with PET or BHET monitored substrate degradation by UHPLC, showing measurable concentrations of TPA, MHET and BHET over six months. 16S rDNA sequencing of the polyps’ microbiomes identified a Pseudomonas strain that grew on multiple polymers; its genome is being sequenced to search for plastic‑degrading enzymes.

Overall, the project identified and characterised over 200 polymer‑degrading enzymes, creating the largest collection of non‑native polymer‑active biocatalysts to date. The collaborative effort combined bioinformatics, molecular biology, microbiology and analytical chemistry, and produced a suite of novel enzymes and microbial strains that hold promise for biotechnological applications in plastic waste remediation.