Perfluoroalkyl substances (PFAS) are strictly manmade compounds that are ubiquitous in environmental systems as a result of use in many industrial and consumer products. They have amphiphilic properties and are expected to partition into cellular membranes where they may disrupt membrane properties. While PFAS have been associated with a variety of biotic effects including an increased susceptibility to co-contaminants, their primary mechanism of action is unknown. It is also unknown if any observed effects on cellular membranes can be translated to impacts on microbial function. A few studies have cited evidence of altered permeability of biological membranes upon exposure to PFAS, though this has not been conclusively demonstrated. A change in permeability could increase or decrease membrane diffusion, having ramifications on microbial functions including quorum sensing and co-contaminant toxicity. Elevated concentrations of PFAS and co-contaminants are often observed in landfills, wastewater treatment plants, and contaminated sites (i.e. military bases) where microorganisms are critical components of waste treatment systems designed to protect human health. Given the importance of microorganisms in nutrient cycling, we studied the effect of PFAS on microbial function and microbial membrane permeability. The effects of PFAS on (1) bacterial membrane partitioning, (2) quorum sensing, and (3) anaerobic digester function were investigated. Results indicate that PFAS partition into microbial membranes, which leads to increased fluidity and permeability; although these effects on cell membranes did not explain all functional changes observed in this study. PFAS partitioned to model membranes and bacteria, where accumulation was a product of the functional group and fluorinated chain length. In model membranes, PFAS increased membrane fluidity in a manner dependent on dose and PFAS characteristics (functional group and fluorinated chain length). Functional changes were observed in a pure culture of a quorum-sensing bacteria, Aliivibrio fischeri. In this case, cultures that were exposed to PFAS were brighter (enhanced quorum sensing function) after a signaling molecule was amended. Increased luminescence was likely a result of increased membrane permeability, resulting in increased diffusion of the signaling molecule. Effects on luminescence were detected at 10 μg/L in PFAS containing eight fluorinated carbons. Lastly, in a mixed anaerobic digester community, the presence of PFAS and aqueous film forming foam, a product that contains g/L concentrations of PFAS, inhibited methane production and the degradation of a co-contaminant, 2,4-dichlorophenol. In each study, the observed effects were correlated to the functional group and fluorinated chain length and were generally only observed when PFAS was present at concentrations greater than 50 mg/L. Results from this study will help the scientific community better understand the range of microbial effects associated with PFAS exposure and the primary PFAS chemical characteristics associated with effects (i.e. the functional group and chain length).
University of Minnesota Ph.D. dissertation. September 2017. Major: Civil Engineering. Advisors: Paige Novak, Matt Simcik. 1 computer file (PDF); ix, 159 pages.
Impact of Perfluoroalkyl Substances on Microbial Membranes and Microbial Functions.
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