Numerous chemical additives lower the freezing point of water, but life at sub-zero temperatures is
sustained by a limited number of biological cryoprotectants. Antifreeze proteins in fish, plants, and insects provide
protection to a few degrees below freezing. Microbes have been found to survive at even lower temperatures, and
with a few exceptions, antifreeze proteins are missing. Survival has been attributed to external factors, such as the
high salt concentration of brine veins and adhesion to particulates or ice crystal defects. We have discovered an
endogenous cryoprotectant in the cell wall of bacteria, lipoteichoic acid biopolymers. Adding 1% LTA to bacteria
cultures immediately prior to freezing provides 50% survival rate, similar to the results obtained with 1% glycerol.
In the absence of an additive, bacterial survival is negligible as measured with the resazurin cell viability assay. The
mode of action for LTA cryoprotection is unknown. With a molecular weight of 3-5 kDa, it is unlikely to enter the
cell cytoplasm. Our observations suggest that teichoic acids could provide a shell of liquid water around biofilms
and planktonic bacteria, removing the need for brine veins to prevent bacterial freezing.