- Title
- PlastiBiome: unravelling the interaction of microorganisms with plastics and its environmental implication
- Creator
- Bhagwat, Geetika
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The ubiquitous presence of plastics in the marine environment is a major global concern due to their environmental persistence and unknown long-term impacts on planetary health. Thousands of tons of plastics, which are currently residing in the world’s oceans, provide an ideal surface for microbial colonisation. This raises questions surrounding the impact of plastic-associated biofilms on the physicochemical, biological and ecological interactions of plastics in the marine environment. Despite the well-established role of microbial biofilms in nutrient cycling, food-web interactions, contaminant transformation and biogeochemical cycles, the potential impact of plastic-associated biofilms in altering the total vector potential of plastics has been underestimated. This PhD is the first comprehensive investigation of i) the onset of plastic-associated biofilms by examining surface conditioning, ii) the composition and functional potential of the plastic-microbiome on different plastic materials, (iii) the diversity and contaminant accumulation potential of biofilms formed on long-term aged plastics aged in intertidal, subtidal and sediment-buried marine habitats and (iv) the changes in the kinetics of contaminant adsorption potential of plastics due to the presence of biofilms in marine conditions; using multidisciplinary approaches. To investigate the conditioning films, which support the onset of biofilms, non-biodegradable Polyethylene Terephthalate (PET) and biodegradable Poly-lactic acid (PLA) plastics were incubated in the natural marine water for 24 h. The surface conditioning was characterised by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). After the 24 h surface conditioning, AFM indicated an increase in the surface area, and the SEM images revealed the adhesion of bacteria. Accumulation of a variety of elements including Nitrogen, Magnesium, Phosphorous, Calcium, Sodium was shown in the EDS analysis, which indicated the precipitation of salts present in the marine environment. Results also indicated that the increase in surface roughness due to surface conditioning depends on the innate roughness and hydrophobicity of plastic polymers. A whole-genome sequencing approach was undertaken to identify the microbial composition and enriched genes in the biofilms formed on four types of microplastics (MP <5mm) viz. Polypropylene (PP), Polyvinyl Chloride (PVC), Polystyrene (PS) and biodegradable Polycaprolactone (PCL) incubated for 8-weeks in Lake Macquarie, NSW, Australia. Taxonomic diversity analysis of the plastic microbiome indicated unique microbial profiles and niche partitioning among the four plastic types. Further, the abundance of marine pathogens on the incubated microplastics, including Vibrio alginolyticus and Vibrio campbellii, indicated that the microplastic contamination could pose a serious threat to marine biota and the food web. The abundance of microbial genera associated with xenobiotic compound degradation, carbon and nitrogen cycling, etc. indicated the potential role of the plastic microbiome in the transformation of environmental contaminants and biogeochemical cycles. Investigation of the KEGG orthologs and UniRef sequences revealed the enrichment of genes involved in type IV secretion system, conjugal transfer protein, plant-pathogen interaction, and heavy metal efflux transfer proteins, revealing the variety of process operated by the plastic-microbiome. The study provided a detailed characterisation of the rapidly altering microbial composition and gene pools on plastics and added new knowledge surrounding the environmental consequences of marine plastic pollution. The composition of established microbial communities associated with High-Density Polyethylene (HDPE) plastic sleeves aged for over 10-years in the intertidal, subtidal and sediment-habitat of an oyster aquaculture farm was examined. In addition, the differences in the surface properties and profiles of metal(loid)s, polyaromatic hydrocarbons (PAHs) and per-fluoroalkyl substances (PFAS) in the plastic associated Inorganic and Organic Matter (PIOM) from the different habitats were examined. Distinct differences were observed in the microbial taxonomic diversity on the HDPE segments from the three habitats and segment type was the defining factor of the community taxonomic variation. High accumulation of PAHs and PFAS along with the presence of pathogenic bacterial genera including Vibrio, Shewanella, and Psychrobacter associated with the PIOM of the aged HDPE indicated potential risks associated with the use of plastics in aquaculture settings. This was the first study to fingerprint the PIOM, provide new information on the partitioning of contaminants to the biofilms and offer insight into the mechanisms underlying the vector potential of plastics in the marine environment. To understand the role of biofilms in altering the potential of MPs to act as a vector for pollutants, the kinetics of Lead and Perfluorooctane Sulfonate (PFOS) adsorption on virgin and biofilm-covered microplastic fibres aged for 26 weeks in the marine environment was investigated. The surface of virgin and naturally aged biofilm-covered polyethylene (PE), polypropylene (PP), Polyester (PES) and Nylon (PA) microplastics were visualised using Scanning Electron Microscopy (SEM) and the biomass was estimated by the crystal violet assay. The global elemental composition was determined by the Energy Dispersive Spectroscopy (EDS) and the surface area and porosity were analysed. Batch adsorption kinetics and adsorption isotherm experiments were conducted to compare the adsorption capacities of virgin and biofilm-covered microplastics. Results indicated that the presence of biofilms on MPs enhanced the adsorption capacity of lead in all biofilm-covered samples and followed the order PA > PES > PP > PE. Higher PFOS adsorption capacity was found in biofilm-covered microplastics compared to their virgin counterparts and followed the order PA>PP>PES>PE. The highest adsorption capacity of lead and PFOS was 0.2 mg.g-1 and 6.3 mg.g-1 respectively associated with biofilm-covered nylon microplastics that are frequently used in textiles industries. The investigation of plastic-biofilm-contaminant interactions carried out in this study adds a significant body of knowledge on the composition and function of biofilms in altering the behaviour of plastics in the marine environment. Overall, the findings from this research will aid environmental risk assessments of plastics and provide a better appreciation of the potential risks of plastic-associated microbial biofilms in the trophic transfer of contaminants in the aquatic ecosystem and for human health.
- Subject
- plastic pollution; microplastics; plastisphere; biofilms on plastics; contaminant adsorption; conditioning films; metagenomics; aquatic pollution; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1500917
- Identifier
- uon:55037
- Rights
- Copyright 2021 Geetika Bhagwat
- Language
- eng
- Full Text
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