INHIBITION OF BACTERIAL CELL GROWTH BY 136 gc MICROWAVES

[NATURE, VOL. 218, APRIL 27, (# 5139) 1968, p. 374-375]

S.J.Webb, D.D.Dodds

During investigations into the effects of dehydration on airborne cells, a millimeter microwave spectrometer, built to measure the quantity of water present in airborne cells, revealed that microwaves had an effect on cell metabolism. We report here some preliminary findings.

Cells of Escherichia coli B grown in nutrient broth were collected by centrifugation, washed twice m 0-85 per cent NaCl and resuspended in fresh nutrient broth to a concentration of 1 x 10⁴ cells/ml. Aliquots of 0-2 ml. were placed in small flat-bottomed vials of 1.0 cm diameter and the vials, either immediately or after set incubation times at 137° C, were placed on the top of a microwave horn and these cells exposed to 136 gc microwaves for periods of up to 4 h. The vials were periodically shaken by hand and the temperature was kept constant with a cooling fan. A small thermocouple was placed in a vial containing nutrient broth only after set periods of irradiation to record the temperature in the vials. The microwaves were produced by use of a 4 mm Philips DX151 Klystron and an FXR harmonic generator, tuned and detected by FXR 2 mm microwave components. The power of the 136 gc microwaves propagated was estimated to be about 7 µW. A full description of the apparatus will be published when the current more detailed studies have been completed. After set times of exposure, 0.8 ml. of nutrient broth was added to the vials, serial ten-fold dilutions made, and 0-2 ml. of each dilution plated on nutrient agar. Colony counts were made after a 24 h incubation at 37° C.

S.Sit’ko, V.Zhukovsky, S.Webb [Kiev, 1989]

The results shown in Table 1 demonstrate that if the washed cells were immediately exposed to the microwaves no cell divisions occurred.

Treatment 0 30 60 90 120 150 180 210 240 Irradiated (lag phase) 125 121 142 136 124 135 123 134 129 Control (lag phase) 131 136 129 138 204 263 412 506 810 Irradiated (log phase) 142 163 211 251 284 286 283 281 288 Control (log phase) 126 184 241 241 462 673 998 1340 1960 Temperature (oC) 25.2 25.2 25.4 25.6 25.8 25.7 25.8 25.9 25.8

The radiation, however, were not lethal because the cell count showed no decrease during 4 h. If the cells were incubated in nutrient broth for 90 min before exposure to the radiations, inhibition of cell divisions was not immediate, and the number of cells/ml. continued to increase until it had approximately doubled. A comparison of the two sets of data suggests that the micro waves have two effects − to slow down cell division and to inhibit specifically metabolic process occurring during the early part of the life span of a cell.

Departments of Bacteriology and Electrical Engineering,
University of Saskatchewan,
Saskatoon, Saskatchewan.

received February 22, 1968