An infrared study of the influence of growth media and myo-inositol on structural changes in DNA induced by dehydration and ultraviolet light

The infrared spectra of films of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and synthetic polynucleotides have been studied under varying degrees of relative humidity (R.H.) in the presence and absence of myo-inositol. In addition the effect of 2537 Å light (ultraviolet) on the hydration of DNA has been investigated. As other researchers have shown, when the R.H. is lowered shifts in the P=O and C=O absorption frequencies occur. These shifts seem to be associated with the removal of approximately 12 molecules of water/nucleotide and all are prevented by the presence of 2 molecules of inositol/nucleotide during desiccation. The irradiation of DNA at 75% R.H. with ultraviolet also produces spectral shifts which appear to arise as a result of bound water molecules moving from P=O and C=O groups.The response of bacterial DNA to desiccation appears to depend on the medium in which the cells are grown. The DNA from cells grown in a minimal salts medium is less hydrated at a given R.H. level than the DNA from cells grown in an enriched medium. This loss of water-adsorbing sites is considered to be due to a physiological replacement of water on the DNA of cells grown on minimal salt medium by amino acids or proteins. RNA and polynucleotides are less hydrated than DNA, which is assumed to be due to their lack of an ordered double helical structure. Of the synthetic polynucleotides poly-I was found to most closely resemble the behavior of DNA. The ability of inositol to prevent spectral shifts in DNA caused by desiccation and irradiation tends to substantiate the suggestion that it preserves the biological integrity of cells and viruses during stress by combining with DNA.

Infrared studies of DNA, water, and inositol associations

Ultraviolet and polarized infrared spectra of oriented films of bacterial DNA have been recorded over a range of relative humidities (R.H.) between 10 and 84%. The films were made from a DNA gel in H2O or D2O with and without 5% (w/v) myo-inositol. In the absence of inositol a large decrease in the dichroic ratio at 1670 cm−1 occurred as the R.H. was lowered between 70 and 30%, indicating the occurrence of considerable disorganization. This was not observed when the DNA was dehydrated in the presence of myo-inositol. A marked increase in absorbance at 2600 Å which occurred on lowering the R.H. from 70 to 50% was prevented also by inositol.These results indicate that myo-inositol can replace water molecules and maintain the DNA in the B configuration during dehydration. The possible significance of these observations in the explanation of certain biological phenomena is discussed.

Lethal and mutagenic action of 3200-4000 A light

Cells of a thymine-requiring auxotrophic mutant of Escherichia coli B have been irradiated with 2537 Å light (ultraviolet) and 3200–4000 Å light (black light) while being held in aerosols of various relative humidity (R.H.) levels. When cells were held in aerosols of 70% R.H. or lower they became susceptible to damage by black light and much of this damage could be prevented by the compound myo-inositol. The damage inflicted on cells by black light was not photorepairable by the usual methods, suggesting that the lesions produced are different from those produced by ultraviolet light. In addition, the ability of cells to undergo photorepair after irradiation with 2537 Å light was found to decrease rapidly when the cells were irradiated in a dry or near-dry state, indicating that the lesions produced under these conditions are different from those produced in wet cells.Sensitization of the cells to both kinds of radiations by the presence of bromodeoxyuridine (BUDR) in their deoxyribonucleic acid was apparent only when the cells were irradiated in a wet or semidry state, suggesting that sensitization involves a photostimulated hydrolysis of BUDR. Black light was found to be more mutagenic to cells held in a semidried state than was 2537 Å light. It is concluded that the irradiation of cells with 2537 Å light or with black light when they are in the dry state produces a lesion which is non-photorepairable and which is both lethal and mutagenic.

The effects of mutation and nucleic acid base analogues on the sensitivity of E. coli to partial dehydration

Investigations have been carried out on the effect of mutation and the incorporation of base analogues into the deoxyribonucleic acid (DNA) of cells on their resistance to dehydration. Auxotrophic mutant cells have been found to possess the same sensitivity or a greater sensitivity than the parent prototrophic organism. This suggests that mutant cells, previously found in populations surviving periods of desiccation, occurred as a result of induced mutation and not the concentration of mutants existing in the cell population before its dehydration. In addition, the incorporation of nucleic base analogues into the DNA of cells has been found to alter their sensitivity to dehydration. With some analogues, the sensitivity of cells is increased and with others it is decreased. Also, the presence of nucleic acid base analogues in the DNA of cells markedly inhibits the ability of myo-inositol to protect cells against dehydration damage. These results suggest that the dehydration of cells is mutagenic and inositol is able to preserve the integrity of desiccated cells by combining with specific areas of normal DNA.

The influence of cell water content on the inactivation of RNA by partial desiccation and ultraviolet light

The influence of the water content of cells of Escherichia coli K38 and Escherichia coli B on the inactivation of F2 phage RNA and β-galactosidase mRNA by partial desiccation and 2537 Å ultraviolet light (uv.) has been studied. Both types of RNA were found to resist desiccation and their inactivation by ultraviolet to require much larger doses than the destruction of the colony-forming ability of cells. The ability of non-induced cells to produce β-galactosidase was destroyed by desiccation and irradiation more easily in non-induced cells than in preinduced cells. The inactivation of RNA was found to occur more readily when the cells contained from 10 to 15 g H2O/100 g of cell solids than when the cells contained less water. Damage by desiccation and irradiation, however, was partially prevented by i-inositol.It is concluded that damage to existing cell RNA either by ultraviolet or desiccation is not involved in the loss of cell viability and that cell death occurs as a result of damage to the mechanism by which mRNA is manufactured.

The influence of oxygen and inositol on the survival of semidried microorganisms

Oxygen was found to have no effect on the induction of the λ prophage due to desiccation but enhanced cell death and the inactivation of the intracellular phages at relative humidity (R.H.) levels below 40%. The magnitude of the oxygen effect increased as the R.H. below 30% decreased. Inositol prevented cell death and phage inactivation due to both bound water reorientation and oxidations. Cells freeze-dried before aerosolization were more stable to storage in air at 30% R.H. and below than they were at 40% to 70% R.H. However, most of the killing of pre-dried cells held at 20% R.H. and below in air was found to be due to an effect of oxygen.

Some observations concerning DNA and beta-galactosidase synthesis in Escherichia coli B

When starved cells of thymine-requiring Escherichia coli B were placed in a complete induction medium there was an initial lag of 10 minutes before measurable amounts of the enzyme were detected. Cells exposed for 15 minutes to one inducer and then given an alternative inducer continued to manufacture the enzyme for 60 minutes at a rate characteristic of the initial inducer. After this period, enzyme manufacture assumed the characteristics of the second inducer. Glucose or mitomycin was found to inhibit enzyme synthesis only when they were added during the first 10 minutes or 45- to 60-minute periods of induction. Chloramphenicol stopped enzyme synthesis at any stage of induction. The synthesis of DNA was found to occur in two stages and enzyme synthesis was prevented by glucose or mitomycin only if they were added to the cells during a 10-minute period which immediately preceded DNA replication. It is concluded that a gene can express itself only once, and change in expression requires the synthesis of new DNA.

A histone-like fraction bound to lipid in Staphylococcus epidermidis

The protein moiety of a proteolipid extracted from Staphylococcus epidermidis has been isolated. It was found to be highly basic, with lysine accounting for 25% of its amino acids. In vitro experiments showed that it readily formed a complex with DNA or RNA. The possible role of this protein fraction in cell stability and the Gram staining reaction is discusssed.