Characterization of the restricted rotation of the dimethyl groups in chemically N-terminal 13C-labeled antifreeze glycoproteins: a temperature-dependent study in water to ice through the supercooled state

Bacterial lipoteichoic acid enhances cryosurvival

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. We show that lipoteichoic acid (LTA), a biopolymer in the cell wall of Gram-positive bacteria, can be added to B. subtilis cultures and increase freeze tolerance. At 1 % w/v, LTA enables a 50 % survival rate, similar to the results obtained with 1 % w/v glycerol as measured with the resazurin cell viability assay. In the absence of added LTA or glycerol, a very small number of B. subtilis cells survive freezing. This suggests that an innate freeze tolerance mechanism exists. While cryoprotection can be provided by extracellular polymeric substances, our data demonstrate a role for LTA in cryoprotection. Currently, the exact mode of action for LTA cryoprotection is unknown. With a molecular weight of 3-5 kDa, it is unlikely to enter the cell cytoplasm. However, low temperature microscopy data show small ice crystals aligned along channels of liquid water. Our observations suggest that teichoic acids could protect liquid water within biofilms and planktonic bacteria, augmenting the role of brine while also raising the possibility for survival without brine present.

Cooperative Hydration of Pyruvic Acid in Ice

About 3.5 +/- 0.3 water molecules are still involved in the exothermic hydration of 2-oxopropanoic acid (PA) into its monohydrate (2,2-dihydroxypropanoic acid, PAH) in ice at 230 K. This is borne out by thermodynamic analysis of the fact that QH(T) = [PAH]/[PA] becomes temperature independent below approximately 250 K (in chemically and thermally equilibrated frozen 0.1 < or = [PA]/M < or = 4.6 solutions in D2O), which requires that the enthalpy of PA hydration (DeltaHH approximately -22 kJ mol(-1)) be balanced by a multiple of the enthalpy of ice melting (DeltaHM = 6.3 kJ mol(-1)). Considering that: (1) thermograms of frozen PA solutions display a single endotherm, at the onset of ice melting, (2) the sum of the integral intensities of the 1deltaPAH and 1deltaPA methyl proton NMR resonances is nearly constant while, (3) line widths increase exponentially with decreasing temperature before diverging below approximately 230 K, we infer that PA in ice remains cooperatively hydrated within interstitial microfluids until they vitrify.