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) a-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.

Characterization and DNA Stable-Isotope Probing of Methanotrophic Bioaerosols

“…This aging process is driven by a variety of physical and chemical processes, all of which can affect the particle size and viability of the microbes ( 51 , 52 ). For instance, the viability of Escherichia coli in a rotating drum was affected by solar radiation, humidity, ozone, and VOCs, which are part of the aging process in the alfresco atmosphere ( 53 ). In the experiments described here, bioaerosols were incubated in the dark, so humidity may be the primary environmental factor affecting the airborne cells in our study.…”

Characterization of single fungal aerosol particles in a reactive atmospheric environment using time-resolved optical trapping-Raman spectroscopy (OT-RS)

“…25,26 Single-particle measurements by scanning Raman spectra of single pollen grains placed on a substrate have been reported, 27,28 but for bioaerosols, properties can dramatically change when they are released into air. 24,[29][30][31] Chemical properties may change through reactions with atmospheric molecules and air pollutants. For example, the structure of lipids, proteins, and polysaccharides in some bioaerosols can be modied when the bioaerosols are exposed in an environment containing O 3 , 32 and even new chemicals may be produced through O 3 oxidation processes.…”

A Collection of Molecular Fingerprints of Single Aerosol Particles in Air for Potential Identification and Detection Using Optical Trapping-Raman Spectroscopy

“…In this case, the sample's properties may be changed in the sampling procedures, and interference may be introduced by interactions between the particle's surface and its surrounding. Additionally, aerosol particles dispersed in air are in an extremely low concentration; thus, measurement of these aerosol particles often requires the collection of sample particles in a sufficient sample volume [20,21], and this resulting measurement may yield different information than that carried by the individual particles. Furthermore, physical and chemical properties of aerosol particles in air are changing all the time due to change in humidity, temperature, or chemical reaction with atmospheric molecules and air pollutants [22][23][24][25][26][27].…”