IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-33, NO. 11, NOVEMBER 1986 Effect of Millimeter-Wave Irradiation on Growth of Saccharomyces cerevisiae LUCIANO FURIA, MEMBER, IEEE, DOUGLAS W. HILL, AND OM P. GANDHI, FELLOW, IEEE Abstract-Cultures of Saccharomyces cerevisiae were exposed for 4 h to millimeter waves in three frequency ranges between 41.650 and 41.798 GHz. The irradiation frequency was stabilized to within ±50 Hz. The temperature difference between irradiated and sham-irradi- ated samples was maintained to within ±0.01°C. Growth was mea- sured optically during the irradiation, and viability counts were done at the end of the irradiation. At least three experiments were per- formed at each of 15 frequencies. No differences larger than ±4 percent were detected in the growth rates at any of the selected frequencies. Such differences were not sig- nificant at the 95 percent confidence limit. Results obtained with plate counts correlated favorably with the optical absorbance data. While our data are in contrast with those reported from other investigators, these experiments support conclusions of our previous studies, and of some other investigators, showing that, under strictly controlled con- ditions, no statistically significant nonthermal effects can be induced by millimeter-wave irradiation of a variety of prokaryotic and eukar- yotic cells. INTRODUCTION S INCE 1968 several investigators have reported a va- riety of biological effects induced by irradiation with millimeter waves (mm-waves). Many have further claimed strong dependence on the irradiation frequency. Representatives of these findings include effects on growth rates of Rhodotorula rubra [1], Saccharomyces cerevisiae [2]-[6] Escherichia coli [7], [8], Candida albicans [1], [9], reduced viability in Sacch. cerevisiae [10], protection of rabbit bone marrow cells from X-ray damage [11], in- creased colicin [12] and lambda phage induction in E. coli [13], and puffing of giant chromosomes of Acricotopus lucidus, an insect [14]. Some reports indicated changes in the magnitude of the effect when the frequency was shifted by a few mega- hertz. Furthermore, some reports were characterized by the low power densities needed to induce the effect; a power density as low as 10 ,tW/cm2 was reported to effect colicin induction in E. coli [12]. An extensive review of the published literature can be found in [15]. Unfortunately, many of the above mentioned reports lack essential details of the experimental procedure and data, making independent duplication or evaluation quite difficult. Some of tnem, however, have been indepen- Manuscript received August 1, 1985; revised June 30, 1986. This work was supported by the U.S. Air Force under Contract F33615-84-K0613. L. Furia has also been sponsored by a travel grant from the Fulbright-Hays Commission for Cultural Exchanges between the United States and Italy. L. Furia and 0. P. Gandhi are with the Department of Electrical Engi- neering, University of Utah, Salt Lake City, UT 84112. D. W. Hill is with the Department of Cellular, Viral and Molecular Biology, University of Utah, Salt Lake City, UT 84112. IEEE Log Number 8610333. dently repeated, mostly with negative findings. Some of the negative experimental results include: no effects on growth rate of E. coli [16] and no changes in viability of Sacch. cerevisiae [17]. No evidence of cytological effects as determined by electron microscopy [18], and in protein synthesis [19] were observed in BHK-21 cells exposed to 202 frequencies in the E- and U- band at various power densities. Finally, no statistically significant effects were found on colicin induction [20], [21], on mutation rates of Salmonella typhimurium or on induction of lambda phage in E. coli by U- and E-band mm-wave irradiation [22], [23]. A strong dependence on irradiation frequency of the growth rate of yeast suspension has been reported inde- pendently by two research groups. Devyatkov [1] re- ported increases up to + 30 percent in the growth rate of R. rubra exposed for 15 h at 7.18 mm (41.783 GHz) and a decreased growth rate of up to -40 percent when ex- posed at 7.19 mm (41.725 GHz). However, no indica- tions were given about experimental procedures such as irradiation conditions, handling of the controls, tempera- ture control and measurement, frequency stability, and power density. Grundler, Keilmann, and co-workers [2], [6] have also reported that the irradiation of Sacch. cerevisiae in the 41.650-41.800 GHz range, showed both growth enhance- ment (up to + 15 percent) and growth. inhibition (down to -13 percent) frequency regions. Frequencies exhibiting significantly different effects were reported to be only 8 MHz apart. The data suggest that the yeast suspensions showed a sensitivity to frequency changes of less than 1 part in 5000. Due to this reported frequency dependence, this phenomenon has been termed a "resonant effect" [2]- [6]. Although such reported frequency sensitivity has stim- ulated interest in the possible mechanism and site(s) of action of mm-waves [18]-[23], [24], [25], it is essential to establish the validity of these observations and their interpretation. In the following we report on our experi- ments designed to study further the possible effects of mm- waves on the growth of Sacch. cerevisiae. MATERIALS AND METHODS A. Description of the Irradiation Experiment The organism used in this study was obtained from the University of Utah stock collection, grown on Sabouraud 0018-9294/86/1100-0993$01.00 © 1986 IEEE 993