Impact of Perfluorinated Organic Acids on Bacterial Ice Nucleators

Perfluorinated acids such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) constitute major environmental pollutants with largely unknown effects on biological ice nucleators (INs), which are crucial for freezing-associated processes in nature. One of the most efficient and abundant INs are bacterial ice-nucleating proteins (INpros). Their record-breaking freezing efficiency relies on assembling large functional aggregates, which, while highly active, show high sensitivity to environmental conditions. This study demonstrates that PFOS and PFOA destroy INpro aggregates, significantly reducing the bacterial ice nucleation efficiency near 0 °C. Exposure to perfluorinated compounds at concentrations of 10 mg/L is sufficient to alter the bacterial IN activity and make them highly unstable toward repetitive freezing. We propose that the adverse effects are based on a coupled mechanism that interrupts attractive electrostatic interactions relevant for INpro multimerization by proton-mediated charge screening, direct electrostatic interference by deprotonated PFOS and PFOA headgroups, and perturbation of the assembly-facilitating bacterial membrane. Our findings contribute to evaluating the ongoing environmental risks of perfluorinated compounds and their effects on related ecological and atmospheric processes.