Characterisation and plastic-degrading potential of plastisphere-associated microorganisms

The versatility and affordability of plastics have contributed to their largely unrestricted production, increasing from two million tons (Mt) in 1950 to roughly 400 Mt per annum in 2022. Consequently, plastic waste is accumulating in the environment, where its degradation is slow, impacting macrofauna. While the details of how plastics affect microorganisms are less well documented, microbes that inhabit the plastic’s surface, termed the ‘plastisphere’, are suggested to have unique functional properties, including the possession of plastic-degrading genes, making microorganisms a vital tool in bioremediation practices. We collected biofilms from a range of different plastics (linear low-density polyethylene [LLDPE], polyamide-6 [PA6], polyethylene terephthalate [PET] and polylactic acid [PLA]), that had been purposely inoculated in aquatic environments, and (i) compared the degradation potential of bacterial isolates, the (ii) influence plastic leachates have on microbial communities, and the (iii) functional potential of the plastisphere, including its potential for plastic degradation, via shotgun metagenomic sequencing. We were unable to isolate any microbial degraders of homochain plastic polymers. Marine bacterial isolates demonstrated surface erosion on LDPE films but failed to produce clearance zones or weight loss in plastic films, both common methods in delineating plastic biodegradation. Marine microbial communities exposed to the leachate of a more biologically degradable polymer, PLA, differed significantly in composition from other plastic-leachate-exposed communities. PLAleachate-exposed communities contained a higher proportion of Proteobacteria, specifically Halomonas spp., reported to degrade LDPE and common plasticisers. Despite these findings, the greatest impact on microbial functional diversity was related to seasonal variation and depth of the plastic; plastic type did not significantly impact microbial community functional traits. This thesis advances our understanding of the influence plastics have on microbial communities. Microorganisms have the potential to adapt to novel environments. However, we find little evidence of microorganisms being able to degrade homochain polymers. Instead, heterochain polymers are far more likely to be degraded and influence community composition through leaching, while plastics serve as a substrate for the dissemination of functional traits, e.g. antimicrobial resistant. This thesis demonstrates the influence plastics have on microbial communities and highlights the need to develop alternative plastics and waste management practices.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Biological Sciences

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2024

Author dc:creator

• Maday, Stefan Dafydd Maurice

Advisors dc:contributor.advisor

• Lear, Gavin
• Handley, Kim
• Kingsbury, Joanne

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/70749

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/70749