Microbial Colonisation and Degradation of Plastic Pollution in the Marine Environment

Nawaz, Ahmed (2020). Microbial Colonisation and Degradation of Plastic Pollution in the Marine Environment. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00011e8f


Plastic pollution is ubiquitous in the world’s oceans and is predicted to increase by an order of magnitude by 2025. The environmental impacts of plastic pollution are well documented in terms of its effects on marine animals however, the impact plastic has on the natural physicochemical characteristics of seawater and the microbial composition of the world’s oceans remains largely unknown. In particular, the role that microbial communities play in the early stages of colonisation and decomposition requires more attention. In response to this knowledge gap, both laboratory-based and field work experiments were undertaken in order to gain further insights. A microcosm experiment using natural seawater amended with range of plastics, both synthetic and biodegradable, was carried out to evaluate the impact of these plastics on the marine microbial communities. To complement this, a one-year field exposure trial was undertaken to measure biofilm formation and growth, as well as changes in polymer characteristics resulting from degradation. Finally, a biodegradation study was undertaken to identify bacteria within seawater that may degrade plastic.

The characterisation of marine bacterial communities revealed major shifts in composition when plastics were introduced into seawater. These microbiological shifts were due to changes in the concentration of dissolved organic carbon, pH and total nitrogen due to the degradation of plastic materials. Furthermore, the long-term field work exposure experiment showed that different plastic substrates selected for distinct colonising communities on their surfaces. The analysis of the biofilm communities revealed the presence of bacteria that could possibly be involved in the degradation of plastics. However, no significant degradation was measured for the in situ tested plastics, suggesting that biofilm formation may have limited degradation. An exploration of plastic degradation using distinct bacterial consortia isolated from seawater resulted in biodegradation (mineralisation) figures of 16, 9 and 7 % for polyvinyl chloride, high-density polyethylene and polyethylene terephthalate respectively.

In summary, results from this thesis suggest that the presence of plastic in seawater affects the microbial community by changing the inherent chemical and biological properties of the water. In addition, plastics were shown to select for distinct colonising communities, which did not contribute to the plastic degradation. However, enriched marine bacterial communities demonstrated biodegradation ability that could be explored further in the future to gain additional insights into underlying biodegradation mechanisms.

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