What are INPs?
Like aerosols or other particles in the clouds, ice-nucleation active (INA) bacteria are types of bacteria that can nucleate ice promoting the growth of water and ice more effectively than any other known material. They use ice-nucleating proteins (INPs) which are attached to their outer membrane. INPs have a β-helical structure, which has been found to be similar to anti-freeze proteins, thus explaining how they might be active under temperature conditions much lower than normal physiological temperature. These proteins can help the bacteria promote ice growth at high sub-zero temperatures which helps these bacteria to gain access to nutrients from plants.
InaZ is such a kind of INP that is found in the INA bacterium Pseudomonas syringae
How do INPs work?
Ice nucleation takes place at the interface of the protein and a few layers of water molecules. It had been reported that an ordered arrangement of water takes place very efficiently at temperatures near the “operating temperature” of the INPs. Interestingly, low temperature increases the inclination of the protein. This increases the surface area of the INA sites that interact with water. With an increase in the interaction of the INA protein sites with water, more water molecules will get arranged in an ordered fashion locally, near the interface. This might be the probable mechanism based on current observation.
Scope and Significance
There is still a dearth of knowledge and experimental data about INP activity, currently. Nonetheless, such studies can be very interesting in understanding how the conformation of these proteins alters while interacting with water at such thin interfaces. This can help us get motivated by such efficient engineering of nature at the molecular level so that we can apply the concept in our man-made designs.
INA bacteria have also been found at high altitudes and even in the clouds. This means they can have huge significance in the causation of cloud glaciation, snow and hail precipitation, and cloud formation. Therefore, their role in regulating the biogeochemical cycles of the earth is pertinent and of great scientific interest.
- Roeters, S.J., Golbek, T.W., Bregnhøj, M. et al. Ice-nucleating proteins are activated by low temperatures to control the structure of interfacial water. Nat Commun 12, 1183 (2021). https://doi.org/10.1038/s41467-021-21349-3