Specific Ion–Protein Interactions Influence Bacterial Ice Nucleation

Abstract

Ice nucleation‐active bacteria are the most efficient ice nucleators known, enabling the crystallization of water at temperatures close to 0 °C, thereby overcoming the kinetically hindered phase transition process at these conditions. Using highly specialized ice‐nucleating proteins (INPs), they can cause frost damage to plants and influence the formation of clouds and precipitation in the atmosphere. In nature, the bacteria are usually found in aqueous environments containing ions. The impact of ions on bacterial ice nucleation efficiency, however, has remained elusive. Here, we demonstrate that ions can profoundly influence the efficiency of bacterial ice nucleators in a manner that follows the Hofmeister series. Weakly hydrated ions inhibit bacterial ice nucleation whereas strongly hydrated ions apparently facilitate ice nucleation. Surface‐specific sum‐frequency generation spectroscopy and molecular dynamics simulations reveal that the different effects are due to specific interactions of the ions with the INPs on the surface of the bacteria. Our results demonstrate that heterogeneous ice nucleation facilitated by bacteria strongly depends upon the nature of the ions, and specific ion–protein interactions are essential for the complete description of heterogeneous ice nucleation by bacteria.

Toward Understanding Bacterial Ice Nucleation

“…Copyright 2020 American Chemical Society. (D) Freezing spectra of P. syringae in pure water and in the presence of 0.5 mol/kg MgSO 4 (purple), NaSCN (blue), NH 4 Cl (red) in water and of NaSCN (light blue), NH 4 Cl (light red) in PBS buffer adapted with permission from ref ( 46 ). Copyright 2021 Wiley-VCH.…”

Membranes Are Decisive for Maximum Freezing Efficiency of Bacterial Ice Nucleators

“…Govindarajan et al further showed that delipidating membranes abolished the activity of class C INs and that the addition of lipids reconstituted activity . A number of studies also revealed that chemicals that disrupt the fluidity of the membrane reduced ice nucleation activity. ,, Recent studies further showed that environmental factors (pH, salts, antifreeze proteins) can have very different effects on class A and class C INs. ,− Here, we use the high-throughput twin-plate ice nucleation assay (TINA) to investigate the ice nucleation activity of the lipids 1,2-dimyristoyl-3-trimethylammonium −propane (DPTAP), 1,2-dipalmitoyl- sn -glycero-3-phosphoglycerol (sodium counterion) (DPPG), 1,2-dipalmitoyl- sn -glycero-3-phosphorylethanolamine (chloride counterion) (DPPE), phosphatidylinositol (PI), lipopolysaccharides, and the effects of deuterated water, heat, and delipidation on the ice nucleation activity of P. syringae …”

“…Our data is consistent with a mechanism, in which bacteria have to exert precise control over (1) the distance between the INP monomers at the sub-Ångstrom level, and (2) the size of the protein assemblies to achieve high ice nucleation activities. 10 This mechanism explains the high sensitivity of class A INs to temperature as well as chemicals 7,11,17,19 that modify the properties of the cell membrane or the aggregation behavior of proteins. Given that highly active class A INs have also been observed in mutated E. coli cells 12 suggests that INP assembly is robust toward variations in exact membrane composition.…”

The effect of (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> on the freezing properties of non-mineral dust ice-nucleating substances of atmospheric relevance

“…Fusarium acuminatum (F. acuminatum) and Fusarium avenaceum (F. avenaceum) have been identified in the atmosphere and have been found to be effective INSs in the immersion mode (Amato et al, 2007;Hasegawa et al, 1994;Pouleur et al, 1992;Richard et al, 1996;Seifi et al, 2014). Cultures were obtained from the American Type Culture Collection (ATCC catalog numbers 60315 and 200466 for F. acuminatum and F. avenaceum, respectively) and grown in potato dextrose broth for 3-4 d at approximately 21 • C shaking at 50 rpm.…”