Absorption of Microwaves by Microorganisms

Abstract

RECENTLY S. J. W. and Dodds reported that 136 GHz microwaves interfere with the growth of Escherichia coli cells¹. Here we report further investigations of the absorption of 65 to 75 GHz microwaves by cells of E. coli B_R as well as isolated protein, RNA and DNA, and its effect on some metabolic processes. Our equipment has been described^1,2. Cells were grown for 24 h at 37° C in nutrient broth (NB) and either (a) washed twice in 0.85 per cent NaCl and deposited as a pellet by centrifugation or (b) resuspended after washing to a cell concentration of 1 × 10⁶ cells/ml. in 0.5 per cent glucose + 0.5 per cent casamino-acids + 50 µg/ml. thymine in 0.1 M phosphate buffer, pH 6.9 (GCT). To examine the effect of microwaves on cell growth, 0.5 ml. aliquots of cells suspended in GCT were placed in vials 1.5 cm in diameter. Some vials were put on top of microwave horns and others incubated at the same temperature (25° C) out of the radiation field. At various times the vials were removed and the number of cells/ml. determined by dilution and plating on nutrient agar. The effect of microwave absorption on metabolic processes was investigated by resuspending the washed cells to a concentration of 1 × 10⁸ cells/ml. in 1.0 per cent glucose in 0.1 M phosphate buffer, pH 6.9. Aliquots of 0.2 ml. of this suspension were placed in the vials and after positioning on the microwave apparatus 0.3 ml. of a solution was added, which contained 0.8 µCi/ml. of one of the following: thymine-2-¹⁴C, uracil-2-¹⁴C or algal ¹⁴C protein hydrolysateplus two of the following: unlabelled thymine, 50 µg/ml.; uracil, 100 µg/ml.; or casamino-acids, 500 µg/ml. After various times the cells from each vial were deposited onto a Millipore filter and washed with 100 ml. of 1 N HCl; the filter was dried and radioactivity counted. The microwave absorption spectra of the cells, H₂O, protein, RNA and DNA were obtained by making films of the material on a thin mica window. The films were dried at 80 per cent relative humidity and covered with a second thin piece of mica. The difference between the microwave absorption of a blank and the film gave the absorption spectrum of the film of cells or biological material.