Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.821122
Title: Food or just a free ride? : exploring marine microbial community dynamics on natural and synthetic polymers
Author: Wright, Robyn Joanna
ISNI:       0000 0004 9358 2002
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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Abstract:
Recalcitrant polymers are widely distributed in the marine environment. This includes natural polymers, such as chitin, but also synthetic polymers such as plastics, which are becoming increasingly abundant and for which biodegradation is uncertain. Distribution of labour in microbial communities commonly evolves in nature, particularly for arduous processes, suggesting that a community may be better at degrading recalcitrant compounds than individual microorganisms. Microbial communities that colonise surfaces and polymers in the marine environment are also known to go through distinct stages of community succession, generally characterised as: i) the attachment phase, defined by an abundance of organisms that are good at colonising; ii) the selection phase, which sees an increase in the abundance of organisms that are good at degrading that substrate; and iii) the succession phase, where efficient degraders are overtaken by cheaters and grazers. Here, it was hypothesised that the general principles of microbial community succession also apply to the colonisation of and growth on, plastics. The majority of studies that investigate the “Plastisphere” – the microorganisms found colonising plastics – examine these at only one time point and the incubation time is often not known, nor whether these communities are degrading the plastics, their associated additives and contaminants, or neither. First, the method of artificial selection was applied to whole microbial communities in order to improve the ability of a microbial community to degrade the natural polymer chitin. It was shown that only when the incubation time was continuously optimised was there an increase in chitinase activity and therefore chitin degradation and this was predominantly due to a shift in the microbial community from the Gammaproteobacteria – active chitin degraders in this case – to the Alphaproteobacteria, which merely possessed the ability to utilise the sub-products of chitin degradation. Application of the artificial selection method requires knowledge of the enzymes used for the process of interest, a high-throughput test for relevant enzymatic activity, knowledge of approximate appropriate incubation times and, as was shown here, constant optimisation of incubation times between selections. Little is currently known about the microbial degradation of plastics in the marine environment, including how long degradation may take and when typical stages of biofilm development occur. Microbial community succession was therefore characterised across six weeks of incubation with different types of polyethylene terephthalate (PET), with the aim of identifying the key stages of microbial community succession. This showed that the communities were more distinct and also enriched with potential PET-degraders, at earlier stages of incubation and had converged by the end of the incubation period, as found in environmental Plastisphere studies when time is examined as a factor. Also, the ability of two marine isolates to degrade PET was characterised using a combined proteogenomic approach and the enzymes used by one of these bacteria to degrade PET were tentatively identified, although the pathway used by the second bacterium was not clear. Finally, the ability of marine bacteria to degrade three common plastic additives, i.e. plasticizers, was also investigated. A proteogenomic approach was again used to characterise the ability of two marine isolates to degrade two phthalic acid ester plasticizers and one citrate plasticizer and this degradation was confirmed by metabolomics. This revealed different mechanisms for the degradation of the two phthalic acid ester plasticizers and also identified tentative mechanisms for degradation of the citrate plasticizer for the first time. This thesis represents a significant step forwards in our understanding of the pathways used for the degradation of recalcitrant compounds by several bacterial isolates, as well as a deeper understanding of the microbial processes and colonisation dynamics that govern the degradation of these compounds in the marine environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.821122  DOI: Not available
Keywords: QD Chemistry ; QR Microbiology
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