Changes of fluorescence spectra and viability from aging aerosolized E. coli cells under various laboratory-controlled conditions in an advanced rotating drum

Abstract

An advanced rotating aerosol chamber was developed to study the changes of fluorescence spectral profile and intensity, the viability and the quantitative polymerase chain reaction (qPCR) signal of Escherichia coli aerosol particles as they are exposed to simulated atmospheric conditions over time. These conditions included relative humidity (RH) below 30% or ∼75%, ozone ∼100 ppb, volatile organic compounds (VOCs) α–pinene (∼5 ppb) or toluene (∼45 ppb), and simulated solar (SS) irradiation. Individual experiments examined the effects of these conditions applied individually and in combination. Experimental results demonstrate that the 263 nm laser excited UV fluorescence band (280–400 nm) showed the greatest rate of decrease, and the visible band (400–580 nm) generally had a smaller change rate which followed the change in the UV band. The 351 nm excited visible band (380–650 nm) had the smallest decay rates, and sometimes increased, when exposed to ozone, high RH, and VOCs. Generally, the viability, qPCR signal intensity, and the fluorescence intensity decayed faster when more variables were applied in combination. Simulated solar irradiation was the most dominant factor in the aging process, followed by the combination of high RH and ozone. Interestingly, the decay of fluorescence and qPCR signal do not appear to correlate directly with loss in viability. Therefore, additional studies are expected to further understand the mechanisms by which atmospheric chemical processes impact viability, qPCR signal intensity, and the fluorescence of biological aerosols.