Browsing by Author "Smith, Katrin Mary Geneve"

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    Characterisation and consequences of urban water resilience at the human-mycobiota interface: risk versus reward
    (Stellenbosch : Stellenbosch University, 2024-03) Smith, Katrin Mary Geneve; Wolfaardt, Gideon M. ; Stone, Wendy; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Urban waters reflect the confluence of microbial ecology and anthropogenic influences. The interactions of microorganisms, chemical micropollutants (MPs) and the surrounding environment require in-depth delineation with a dual purpose. While microbes and MPs can pose risks to humans and ecology, an understanding of physico-chemical, species dynamics and intrinsic MP resilience at the microbial-contaminant interface can benefit future MP attenuation strategies. Therefore, the goal of this research was to characterise and harness urban river microbial and chemical constituents, and the interplay thereof. Moreover, focus was placed on the assessment of fungi and antifungals (AFs), represented by comparatively less literature than bacteria and antibiotics. An environmental survey of representative antifungals in regional rivers revealed nanogram per litre concentrations in alignment with similarly low-risk levels detected globally. Trends reflected agricultural practises and medical use, showing wastewater treatment plant (WWTP) influence on rivers. Bioassays detected androgen (AR) antagonistic and aryl-hydrocarbon receptor (AhR) activity from agricultural fungicides, and AF-MP mixture responses could be attributed to individual effects of carbendazim, dimethomorph, flusilazole and procymidone. Moreover, concentration factors applied to achieve toxicity quantification were ten- to 100-fold higher than the average MP levels detected in local and global waters. This indicates more beneficial bioassay utility for whole effluent or environmental samples with elevated MPs and metabolites, where concentrations are inherently higher than typical river water. Analyses of fungi in riverine consortia revealed limited clinically- relevant taxa that were associated with elevated pollution. The acclimatisation of consortia to sterile river water, containing MPs, in bioreactors favoured community shifts toward environmental rather than opportunistic taxa. Acclimatised microbiota were thereafter exposed to AF and AF-MP mixtures in reactors, the former containing low and the latter 100-fold higher microgram (per litre) concentrations. Fungal numbers increased despite limiting conditions including the presence of inhibitory AFs. After in vitro exposure, AF susceptibility differences were assessed with two medical and agricultural AFs apiece. Inherent levels of resilience in the consortia were apparent, with enhancement observed post-exposure, particularly toward fungicides. This was more evident in communities exposed to sub-inhibitory AFs, compared to the MP mixture, aligning with reports on exacerbated drug-resistance in environmental taxa subject to consistent contact with low-level antimicrobial (AM) and non-AM mixtures. However, despite an increased risk of AFR, the observation of resilience toward MPs demonstrates advantages for environmental consortia in bioremedial applications, as sub-inhibitory exposure does not limit metabolism or survival. As such, MP degradation potential was investigated in continuous flow reactors under environmental conditions. Significantly higher removal rates were observed for inoculated reactors compared to uninoculated controls. Despite the presence of broad-spectrum AFs, the microbiota exhibited higher removal rates for several AFs compared to other MPs. The biological reactors also significantly reduced estrogenicity to below human toxicity thresholds. Although some MP removal rates were lower than reported in exploratory literature on fungal or mixed microbial WW treatments, the aim of this study was to investigate unmanipulated consortia in energy- and cost-effective conditions representing parameters that remain less explored. Field-scale, feasible bioremediation setups are critical for future remediation of anthropogenic pollution and protection of water resources. Urban waters comprise both the natural interplay of microorganisms and MPs in surface waters, and the harnessing of these interactions in engineered ecosystems, including WWTPs. Environmental and manipulated settings apply direct and indirect pressures on microbiota, the consequences of which may be negative or advantageous. Monitoring for MPs, microbes and drug-resistance is important for characterising potential human and ecosystem health risks. On the other hand, the predisposition of microbiota toward MP resilience, and their adaptability to a wide range of conditions, provides opportunity for microbiological applications in MP attenuation. This research contributes toward an understanding of ecological dynamics at the microbial-contaminant interface to help inform the development of energy- and cost- efficient bioremediation strategies.