Electrical charges on airborne microorganisms

We have investigated the parameters affecting the magnitude and polarity of the electric charges carried by biological particles in the airborne state. A recently developed experimental setup through which we analyzed the electric charges imposed on airborne particles by a means of induction charging (Mainelis et al. (Aerosol Sci. Technol. 2001, submitted for publication)) was utilized for this research. In this study, the microorganisms were aerosolized under controlled conditions and an electric mobility analyzer extracted particles of specific electric mobility. The extracted microorganisms were then analyzed by an optical particle size spectrometer. The amount of electric charge carried by airborne microorganisms was found to depend on the dispersion method and can be more than 10,000 elementary electric charges. This finding contrasts with the low electric charge levels carried by non-biological particles. Our data show that repeated pneumatic dispersion of sensitive bacteria affects their structural integrity, which, in turn, changes the magnitude of electric charges carried by these bacteria. We have concluded that the amount of electric charge carried by aerosolized bacteria may be used as an indicator of mechanical stress. It was also found that the electrical conductivity and the pH level of a bacterial suspension increase during aerosolization from a Collison nebulizer. Thus, these two parameters may be used as indicators of the mechanical stress, injury and loss in viability, endured by bacteria during aerosolization, i.e., measuring the electrical conductivity and pH level of bacterial suspensions may be a simple and convenient method for monitoring the "wear and tear" of the bacteria suspended in deionized water.