# Impact of Perfluorinated Organic Acids on Bacterial Ice Nucleators

## TL;DR

This paper shows that perfluorinated acids like PFOS and PFOA disrupt bacterial ice-nucleating proteins, reducing their ability to initiate freezing at low temperatures.

## Contribution

The study reveals a novel mechanism by which perfluorinated compounds impair bacterial ice nucleation through electrostatic and membrane-related effects.

## Key findings

- PFOS and PFOA at 10 mg/L concentrations significantly reduce bacterial ice nucleation efficiency.
- Perfluorinated compounds destabilize ice-nucleating protein aggregates through electrostatic and membrane interference.
- The disruption leads to instability in bacterial ice nucleation under repetitive freezing conditions.

## Abstract

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.