Perfluoroalkyl Substances (PFASs) Partition into Bacterial Cell Membranes and Cause Unexpected Lipid Ordering

Perfluoroalkyl substances (PFASs), commonly found for example in non-stick coatings and waterproof materials, are persistent environmental pollutants that do not degrade naturally within the environment. Referred to as “forever chemicals”, PFASs bioaccumulate across the food chain, binding strongly to proteins and partitioning into fatty regions such as cellular (lipid bilayer) membranes. Specific to membranes, PFASs are known to accumulate in and disorder model membranes comprised of single component, often zwitterionic, lipids. Our goal is to extend PFAS partitioning studies to live, intact bacterial membranes and bacterial membrane extracts to determine how complex lipid mixtures, including anionic lipids that are expected to repel the anionic headgroup of PFASs, respond to PFAS accumulation. Alcanivorax borkumensis, an alkane-degrading marine bacterium, was used as a model organism. A range of carboxylate and sulfonate PFASs were examined at concentrations ranging from nanomolar to micromolar to determine the role of perfluoroalkyl chain length (C₄-C₁₀) and headgroup (COO^- and SO₃^-) on A. borkumensis growth and in situ membrane ordering. This includes the legacy C₈ compounds perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). All PFASs lead to unexpected lipid ordering of the membrane based on fluorescence anisotropy measurements, with longer chain PFASs leading to the greatest ordering. Cell growth also unexpectedly increased in the presence of PFASs, with higher PFAS concentrations leading to greater cell growth. Monolayer studies using A. borkumensis membrane extracts are being conducted to determine why lipid ordering, and possible lipid condensation, is observed for all PFASs examined despite the varying degrees of surface activity.