FT-IR spectroscopic studies on molecular interactions of cryoprotectant agents with bacteria

Fourier transform infrared spectroscopy was used to investigate, without any destructive interference, interactions of the cryoprotective agents, glycerol and dimethyl sulfoxide with Bradyrhizobium japonicum. The intracellular spectrum of glycerol, obtained by subtracting the spectrum of control bacteria from that of glycerol-treated bacteria, showed no differences in infrared features compared to that of pure glycerol. This was not the case when dimethyl sulfoxide treatment was used. The intracellular spectrum displayed important modifications compared to that of the pure chemical. Spectral analysis showed that glycerol and dimethyl sulfoxide uptake required only a few minutes. Moreover, the infrared features resulting from the presence of pure glycerol, in bacteria, were still existent for up to 2 or 3 hours after thawing process. The deconvoluted Amide I and Amide II bands of bacterial proteins reflected important changes in secondary structure after treatment of bacteria with dimethyl sulfoxide (increase in β-sheet and loss of random coil content). In contrast to glycerol, the cryoprotective action of dimethyl sulfoxide probably involves interactions with a wide range of intrabacterial species. © 1995 John Wiley & Sons, Inc.