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Investigating microbial responses to PFOS and PFOA exposure

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Abstract
Per- and polyfluoroalkyl substances (PFAS), a group of synthetic chemicals, known as "forever chemicals" for their exceptional physical and chemical properties, have become a pressing environmental concern due to their persistence and bioaccumulation. This thesis presents a comprehensive investigation into the dynamic interplay between PFAS and microorganisms, employing Escherichia coli as a model system to elucidate the molecular mechanisms governing their impact. Initially, this study investigated the potential biodegradation of the recalcitrant PFAS compound, perfluorooctanesulfonic acid (PFOS), using contaminated landfill leachate for microbial enrichment and Pseudomonas strain isolation. However, no evidence of PFOS degradation was obtained. Next, this work investigated the effects of perfluorooctanoic acid (PFOA) and PFOS exposure on E. coli under various stress conditions (salt and acid stress). Exposure to PFOA affected the growth and survival of E. coli at pH 5.2 and pH 3, respectively. Transcriptomic analyses of PFOA-exposed cells compared to octanoic acid at pH 5.2 as a control further shed light on the underlying molecular mechanisms, revealing distinctive gene expression patterns under these conditions. Notably, higher differential expression of genes associated with acid stress response, membrane disruption, oxidative stress, and DNA damage emerged in PFOA-exposed cells. Finally, an in vitro evolution experiment (IVEE) using E. coli provided further insights into the differential impact of PFOA and octanoic acid on cell growth, survival, and membrane integrity, attributing PFOA's heightened toxicity to membrane disruption. Overall, this study provides essential insights into interactions of PFAS with microorganisms using E. coli as a model, indicating that PFOA exposure can cause significant stress responses in E. coli cells and may exacerbate the effects of other stressors, such as acid stress. Furthermore, this phenomenon may extend to other bacterial species, potentially impacting microbial-based ecosystems. Overall, these findings have important implications for understanding the potential impacts of PFOA exposure on living organisms and the environment.
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Publisher
University of Galway
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Attribution-NonCommercial-NoDerivatives 4.0 International