In a groundbreaking study, researchers have discovered that certain fungi possess the ability to nucleate ice, a capability previously attributed primarily to specific bacteria. This discovery, published in the journal Science Advances, was made by a team from Boise State University and the Max Planck Institute for Polymer Research, led by Konrad Meister. The findings reveal that fungi in the family Mortierellaceae can form ice at higher temperatures, offering new insights into the biological processes of ice formation.
In its purest form, liquid water can remain in a liquid state down to -40°C if undisturbed. However, to freeze water below 0°C, a “template” is needed to arrange molecules in the precise order required for ice to form. While certain bacteria have developed proteins to perform this function, the discovery that fungi can also nucleate ice introduces a new dimension to our understanding of this natural phenomenon.
Unveiling the Ice-Nucleating Ability of Fungi
The research team identified a new class of ice-nucleating proteins in lower fungi, solving a long-standing mystery about how these organisms initiate ice formation. This capability is believed to have evolved through horizontal gene transfer, a process where genetic material moves between unrelated organisms. The genetic blueprint for these proteins likely originated from bacteria, such as Pseudomonas syringae, which possess the InaZ gene known for its ice-nucleating properties.
Meister’s team sequenced the genomes of ice-active Mortierellaceae fungi collected from polar regions, water, and lichens. Their findings revealed genes similar to InaZ, suggesting a shared evolutionary history with bacteria. The fungal gene’s chemical signature more closely resembles bacterial DNA, supporting the theory of horizontal gene transfer.
Differences Between Fungal and Bacterial Proteins
Despite their similarities, fungal and bacterial ice-nucleating proteins exhibit distinct differences. Rosemary Eufemio, a doctoral student at Boise State, noted, “Although they appear similar, they are actually distinct from each other.” Fungal proteins have evolved to be more soluble and stable, advantageous for their ecological niches.
Unlike bacterial proteins, which require a cell membrane to function optimally, fungal proteins can initiate ice nucleation without a membrane. This structural difference allows fungi to form large functional clusters independently, facilitating ice formation at higher temperatures.
Experimental Validation and Environmental Implications
The researchers used artificial intelligence to model the protein structures, discovering that clusters of three to five proteins create a surface area sufficient for ice nucleation. These proteins can nucleate ice at temperatures between -5°C and -8°C, comparable to the best biological ice nucleators known.
To validate their findings, the team transferred fungal genes into yeast and E. coli, organisms that do not naturally form ice. The transformation made them ice-active, significantly increasing their nucleating efficiency. This suggests that fungi could play a crucial role in atmospheric and environmental processes.
Potential Applications in Biotechnology
The discovery of water-soluble, non-membrane-associated ice-nucleating proteins opens new avenues for materials science and biotechnology. These proteins could revolutionize cryopreservation, a field hindered by uncontrolled ice crystal growth during the storage of human cells and tissues. The ability to predictably trigger ice formation at specific temperatures could overcome this obstacle.
Moreover, fungal proteins offer practical advantages over bacterial proteins in Controlled Freezing Technology (CFT). Their solubility and stability make them easier to isolate, handle, and incorporate into various applications, potentially transforming industries reliant on precise ice formation.
Understanding Supercooling and Ice Formation
For those wondering why water can remain liquid at -40°C, the answer lies in the purity of the water. Ordinary water freezes at 0°C due to impurities that act as nucleation sites. In contrast, pure, distilled water can supercool, remaining liquid well below 0°C under controlled conditions. This phenomenon occurs when water is exceptionally purified and isolated from disturbances.
Fungal proteins can trigger ice formation in supercooled water at temperatures as high as -5°C, a remarkable feat for biological ice nucleators. This ability underscores the potential of fungi to influence natural and technological processes involving ice formation.
The study, published in Science Advances, marks a significant step forward in understanding the role of fungi in ice nucleation and their potential applications in various fields.
