Japanese Journal of Freezing and Drying

The preservation of cells and activities of the bacterial strains by L-drying and freeze-drying methods followed 14 day preservation tests at 37℃ were investigated. The cells of nicotine degrading bacteria, Arthrobacter globiformis JTS-6, more survived by L-drying than the cells preserved by freeze-drying, and the survived cells of Pseudomonas putida JTS-9 were twice as many as those by freeze-drying. The nicotine degrading activities of the preserved cells of the two strains were the same as those of original cells, respectively. In the case of the bacterial strain which improves the taste and aroma of cured tobacco leaves, Bacillus pumilus JTS-308, the viable cell number after L-drying was 73% of that after freeze-drying, but its activity for tobacco leaves was completely preserved. The cells preserved by L-drying of the pathogenic bacteria of tobacco bacterial wilt, Pseudomonas solanacearum JTS-338, survived ten time as many the survived cells preserved by freeze-drying, and 100% of the slime forming activity (pathogenicity) was also preserved.

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DNA injury in L-dried Escherichia coli cells was investigated using the alkaline sucrose gradient sedimentation technique. When the cells were dried in 0.1 M potassium phosphate buffer containing 3 % monosodium glutamate, no DNA single-strand breaks were detected immediately after drying, but temperature-dependent DNA breakage were induced during the preservation process in dried cells. Addition of 30mM thiourea or 100mM adonitol into the suspending fluid resulted no significant DNA breaks immediately after drying and after preservation for 6 months at 5℃. After preservation for 8 weeks at 37℃, DNA breaks in cells dried with thiourea or adonitol were apparently smaller as compared with those in cells dried without the protectants. Furthermore, thiourea and adonitol were protected vegetative cells from damage by radicals derived from hydrogen peroxide. From the results, thiourea and adonitol are considered to act as radical-scavenger, and resultant prevention of DNA strand breakage. No evidence for preventing effect of cysteine on DNA strand breakage has been obtained, and role of cysteine in increasing survival of dried cells has not been clear.

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A mechanism of freezing and thawing of gels made from cross-linked dextrans (Sephadex) and water was investigated by using DSC and an ESR spin probe method. We obtained, from DSC, a strong suggestion that compartmentalized water by the network structure formed by cross-linkages of Sephadex G-25 remains unfrozen during cooling and crystallizes during subsequent warming. From ESR studies, however, no evidence which indicates the presence of liquid water was obtained below -50℃ with this gel system. A conceivable mechanism of anomalous crystallization observed with a Sephadex G-25-water system during warming(recrystallization) was proposed referring to changing of the network structure during both of freezing and thawing.

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