ENVIRONMENTAL BIOTECHNOLOGY
Differential gene expression in Escherichia coli during aerosolization
from liquid suspension
Tsz Wai Ng
1
&
Margaret Ip
2
&
Christopher Y. H. Chao
3
&
Julian Wei Tang
4
&
Keng Po Lai
5
&
Sau Chung Fu
3
&
Wing Tong Leung
3
&
Ka Man Lai
1
Received: 12 January 2018 / Revised: 29 April 2018 /Accepted: 8 May 2018 / Published online: 28 May 2018
#
Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
Comparative transcriptome analysis was used to determine the differentially expressed genes in Escherichia coli during aero-
solization from liquid suspension. Isogenic mutant studies were then used to examine the potential part played by some of these
genes in bacterial survival in the air. Bioaerosols were sampled after 3 min of nebulization, which aerosolized the bacteria from
the liquid suspension to an aerosol chamber (A0), and after further 30 min of airborne suspension in the chamber (A30). Bacteria
at A0 showed 65 differentially expressed genes (30 downregulated and 35 upregulated) as compared to the original bacteria in the
nebulizer. Droplet evaporation models predicted a drop in temperature in the bioaerosols, which coincides with the change in the
expression of cold shock protein genes—cspB and cspG in the bacteria. The most notable group of differentially expressed genes
was sorbitol transport and metabolism genes (srlABDEMR). Other genes associated with osmotic stress, nutrient limitation, DNA
damage, and other stresses were differentially expressed in the bacteria at A0. After further airborne suspension, one gene (ypfM,
which encodes a hypothetical protein with unknown function) was downregulated in the bacteria at A30 as compared to those at
A0. Finally, isogenic mutants with either the dps or srlA gene deleted (both genes were upregulated at A0) had lower survival than
the parental strain, which is a sign of their potential ability to protect the bacteria in the air.
Keywords Airborne bacteria
.
RNA-seq
.
Stress response
.
Transcriptome analysis
Introduction
In the prediction of airborne transmission and dispersal of
pathogens from respiratory droplets, certain models have been
proposed to theoretically describe the physical change in the
droplets during evaporation (Gralton et al. 2011; Lighthart and
Kim 1989; Liu et al. 2017;Parientaetal.2011). Although a
number of studies applied different approaches and parameters
in constructing the models, a prediction which has often been
denoted is that water in the newly formed bacterial droplet will
evaporate within milliseconds before reaching equilibrium to
form a stable droplet nucleus in the air (Liu et al. 2017; Parienta
et al. 2011). During evaporation, temperature, solute content,
and other environmental conditions of the droplet may change
depending on various factors such as nebulization conditions
(e.g., nebulization methods, composition of the bacterial sus-
pension, and temperature), air temperature, and relative humid-
ity (RH) (Liu et al. 2017; Parienta et al. 2011). Previously,
Krumins et al. (2014)reportedanincreaseinrRNAgeneex-
pression in an airborne bacterium, Sphingomonas aerolata,in
response to different volatile organic compounds as growth
substrates. However, before the bacteria adapt to such environ-
mental stimulus, they first need to face the rapid and diverse
physical changes in the droplet immediately after aerosoliza-
tion. How the bacteria regulate their gene expression in
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s00253-018-9083-5) contains supplementary
material, which is available to authorized users.
* Ka Man Lai
laikaman@hkbu.edu.hk
1
Department of Biology, Hong Kong Baptist University, Kowloon
Tong, Hong Kong
2
Department of Microbiology, Chinese University of Hong Kong,
Prince of Wales Hospital, Shatin, Hong Kong
3
Department of Mechanical and Aerospace Engineering, Hong Kong
University of Science and Technology, Kowloon, Hong Kong
4
Clinical Microbiology, University Hospitals of Leicester NHS Trust,
Leicester, UK
5
Department of Biology and Chemistry, City University of Hong
Kong, Kowloon Tong, Hong Kong
Applied Microbiology and Biotechnology (2018) 102:6257–6267
https://doi.org/10.1007/s00253-018-9083-5
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