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Abstract
Marine biofouling describes the ubiquitous process of organisms colonising a submerged surface. Biofouling can present problems for both natural and artificial surfaces, including an increase in drag, shading effects corrosion and blocking of intakes. As a result, antifouling strategies have been developed by man and evolved by nature, however the former are usually untargeted biocides and there is a pressing need for a widely applicable environmentally responsible alternative. The living paint system is a biomimetic coating in which a bioactive bacterium is included within an encapsulation matrix, exudes deterrent metabolites, and in theory provides continuous protection from fouling. In this way it mimics naturally occurring bacterial biofilms, which are enclosed in a matrix (EPS) and exude inhibitory compounds.
Chapter 2 of this thesis focuses on the active part of the living paint system which is the encapsulated bacteria. This chapter describes the assessment of a range of epiphytic marine bacteria for their ability to be cultured with the broad spectrum antifouling bacterium Pseudoalteromonas tunicata, as well as for their ability of individual or co-encapsulated strains to inhibit the settlement of two common macrofoulers, the bryozoan, Bugula neretina and the red alga Polysiphonia sp..
The subsequent chapters of this thesis focus on finding an appropriate encapsulation matrix for P. tunicata s release into the marine environment. Chapters 3 and 4 detail the encapsulation of P. tunicata in organic and inorganic encapsulation matrices respectively. P. tunicata was trialled for its ability to survive within these matrices, and using confocal microscopy, their distribution within the matrices quantified, and their ability to inhibit settlement of common macrofouling organisms assessed while encapsulated within these matrices. The matrices themselves were also exposed to macrofiltered seawater to test for their resistance to degradation. Formulations of sodium trisilicate and a hybrid polymer of xanthan and gellan gum performed best amongst the matrices trialled.
Chapter 5 describes testing the living paint system in the field. Testing was carried out with the matrices held within a test apparatus submerged below the low tide mark under a pier. Fouling was recorded as a percentage cover, and also using molecular techniques to measure shifts in the microbial population. A trial of organic matrices found a significant deterrence of fouling by matrices containing P. tunicata after 2 weeks. The matrices degraded before macrofouling could take place.
Novel matrices for encapsulating bacteria were developed in this thesis. In the lab, and to a smaller extent in the field, they inhibited fouling for short periods of time. A key requirement for advancing the living paint system is the development of a stronger matrix for exposure in the field. Notwithstanding this, the technology shows promise and has wider biotechnological applications beyond antifouling.