## 1 Introduction
### MMW Interaction with Water as a Factor for Reduced Cell Growth  
In the above section, the experiment indicated that the MMW irradiation could affect cell growth/division without causing directed DNA molecules damage. However, the radiation may elicit perturbations of DNA regulatory proteins responsible for structural or chemical modifications of the genome and proteins regulating other metabolic processes. This can happen by interaction of the radiation with water, which is well known to absorb electromagnetic radiation in the microwave and infrared spectrum [23], which indirectly can affect protein structure and function. Thus, we examine the amount of MMW radiation, which is solely absorbed by the yeast cells and the part that is reflected. Based on the energy penetrating the cells we may be able to unravel the contributions of MMW interactions with the cytosolic part of the cells, which contains many types of macromolecules. Therefore, we measured the absorbed power over time, represented as a ratio of incident and reflected powers for yeast cells spotted on SC agar. This was compared to that of plain water and blank SC agar without cells respectively. The irradiation conditions were kept constant at 85 GHz for 5 h (5 dBm, at the maximal power level available to us corresponding to 1.39 \(\pm\) 0.02 mW/cm\({}^{2}\)) for stringency of analysis. The sample(s) absorbs a part of the incident radiation and the remaining is reflected. We find that the yeast cells spotted on SC agar absorbed more power (Figure 3) as compared to plain water and blank SC agar without cells on the same volume of media used. Interestingly, plain SC agar reflected most of the incident power. The results suggest that non-thermal exposure of MMW could affect the proteins present in the cytosolic part of the cells through interactions with water molecules without involving heat shock proteins [24]. This could account for the observed phenomenon of cell growth inhibition without genetic perturbation or by damage of other functional cytosolic protein molecules and/or structures (see Figure 2). The experiment also indicates that cells have a high absorbance of MMW irradiation by macromolecules within a cytosol made mostly of water separated from the environment within a confined volume of membrane bound structures. Figure 2: Representative image of the colony growth profiles of WT and \(\Delta\)_rad52_ cells with serial dilutions after (90 GHz) MMW irradiation at 5 dBm for 6 h. The cells were grown under physiological conditions at 30 \({}^{\circ}\)C, over 3–4 days post-treatment period. Number of cells after serial dilutions are as indicated. Five independent experiments were performed. No statistically significant differences were found between the two examined strains. Therefore, in order to ascertain any relation behind MMW absorption, temperature and volume of sample treated as indicated from the previous experiment, different volumes of water were irradiated using the horn antenna and temperature rise monitored. Irradiation conditions of frequency, power and duration of exposure were kept constant as mentioned previously to maintain empirical stringency. A 2 \({}^{\circ}\)C rise of temperature measured using a digital thermometer was associated with a 6 h exposure duration at 1.39 mW/cm\({}^{2}\) from a horn antenna (Figure 4a) on a large volume of water (6500 \(\mu\)L). Reduction in the size of the irradiated sample to a smaller volume of water (250 \(\mu\)L) led to a 1 \({}^{\circ}\)C increase in the rate of temperature rise (Figure 4b). Interestingly, exposure involving a waveguide (delivering a higher power density of 17.17 mW/cm\({}^{2}\)) on the same small volume of water (250 \(\mu\)L) did not change the rate of temperature rise any further (Figure 4c). Further, contrary to the expectation of the waveguide causing thermal ablation due to higher power density, the experiment demonstrates that thermal effects were practically absent in our irradiation setup.