Marine bacteria as a source of polyester-degrading enzymes with biocatalytic potential

dc.contributor.advisorDobson, Alan
dc.contributor.advisorClarke, David J.
dc.contributor.authorCarr, Clodagh M.
dc.contributor.funderScience Foundation Irelanden
dc.contributor.funderSynthesis and Solid State Pharmaceutical Centreen
dc.description.abstractThe issue of plastic waste continues to surge, as does our collective awareness of this global problem and interest in finding sustainable solutions for its control. Bacteria, which are among the earliest known forms of life, have evolved over millions of years to degrade organic matter found in the environment by producing enzymes that can catalyse the breakdown of various compounds for energy and nutrient gain. With biotechnological advances in recent decades, bacterial enzymes have emerged as a tool for the catalysis of chemical reactions, where they can aid in the development of safer, more efficient, and more environmentally friendly processes. The conventional recycling of plastic waste has typically consisted of a thermo-mechanical process, where waste is ground down, melted, and reformed into new, but lower-quality products that are less likely to be recycled multiple times. While alternative chemical methods can improve recyclability by facilitating recovery of the raw materials used to make plastic, enzyme-based treatments enable the same process to be conducted under milder, less energy-intensive reaction conditions without the use of hazardous reagents and solvents. Enzymes that are specialized to break apart ester bond-containing compounds in nature can be employed for the degradation of polyester-based plastics, allowing for the sustainable recycling of these materials after use. Polyester-degrading enzymes (termed polyesterases) have been studied with a particular focus on the recycling of polyethylene terephthalate (PET), a synthetic polyester which is mass-produced for use in food and beverage packaging or as a fiber in the textile industry. By an enzymatic hydrolysis mechanism, the PET polymer may be degraded into its short-chain oligomeric intermediates MHET and BHET and/or its constituent monomers ethylene glycol (EG) and terephthalic acid (TPA) which can subsequently be recycled into PET or upcycled into value-added products. In chapter 1, a literature review was conducted on microbial PET hydrolase enzymes to assess existing knowledge in the field, identify key challenges, and determine important areas for future research. Thermophilic bacteria from the phylum Actinomycetota such as Thermobifida fusca emerged as a major source of PET-hydrolyzing enzymes as well as those with fungal and metagenomic origins, while Ideonella sakaiensis, a mesophilic bacterium isolated from a PET-contaminated site served as a model system featuring both PET and MHET hydrolases predicted to work in tandem. Relatively few PET-hydrolyzing enzymes were reported from marine environments, an aspect which we hoped to expand upon. In chapter 2, activity screening and genome mining of marine bacterial isolates led to the identification of a polyesterase, BgP, from a deep-sea, marine sponge-derived Brachybacterium sp. isolate. BgP was explored as a structural homolog of cutinase-like enzymes, such as Cut190, LCC, and TfCut2, which had previously been reported for efficient hydrolysis of PET and its hydrolytic activity was confirmed on the PET model substrate polycaprolactone (PCL). In chapter 3, PET-hydrolyzing activity was confirmed for SM14est, a marine sponge-derived polyesterase from Streptomyces sp. SM14 with this enzyme exhibiting a preference for high-salt conditions and moderate temperatures (up to 45°C). In chapter 4, MarCE, a marine carboxylesterase was found encoded in the genome of a Maribacter sp. isolated from a sea sponge sample collected at Lough Hyne. MarCE was shown to hydrolyze polycaprolactone diol and putative binding of PET oligomers was demonstrated by molecular docking analysis. The work presented on BgP, SM14est, and MarCE makes a case for the continued exploration of marine-derived bacteria, in particular those found within the unique marine sponge ecosystem, as a source of potentially novel polyesterases with relevance for the biological degradation of synthetic polyesters among other biocatalytic applications.en
dc.description.statusNot peer revieweden
dc.description.versionAccepted Versionen
dc.identifier.citationCarr, C. M. 2023. Marine bacteria as a source of polyester-degrading enzymes with biocatalytic potential. PhD Thesis, University College Cork.
dc.publisherUniversity College Corken
dc.relation.projectinfo:eu-repo/grantAgreement/SFI/SFI Research Centres/12/RC/2275/IE/Synthesis and Solid State Pharmaceutical Centre (SSPC)/
dc.rights© 2023, Clodagh Carr.
dc.subjectEnvironmental microbiologyen
dc.subjectMicrobial biotechnologyen
dc.subjectMarine spongesen
dc.subjectMarine bacteriaen
dc.titleMarine bacteria as a source of polyester-degrading enzymes with biocatalytic potential
dc.typeDoctoral thesisen
dc.type.qualificationnamePhD - Doctor of Philosophyen
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