Title: Activation of intact bacteria and bacterial fragments mixed with agar as cloud droplets and ice crystals in cloud chamber experiments

Abstract

Biological particles, including bacteria and bacterial fragments, have beenof much interest due to the special ability of some to nucleate ice atmodestly supercooled temperatures. This paper presents results from a recentstudy conducted on two strains of cultivated bacteria which suggest thatbacterial fragments mixed with agar, and not whole bacterial cells, serve ascloud condensation nuclei (CCN). Due to the absence of whole bacteria cellsin droplets, they are unable to serve as ice nucleating particles (INPs) inthe immersion mode under the experimental conditions. Experiments wereconducted at the Aerosol Interaction and Dynamics in the Atmosphere (AIDA)cloud chamber at the Karlsruhe Institute of Technology (KIT) by injectingbacteria-containing aerosol samples into the cloud chamber and inducing cloudformation by expansion over a temperature range of -5 to -12°C.Cloud droplets and ice crystals were sampled through a pumped counterflowvirtual impactor inlet (PCVI) and their residuals were characterized with asingle particle mass spectrometer (miniSPLAT). The size distribution of theoverall aerosol was bimodal, with a large particle mode composed of intactbacteria and a mode of smaller particles composed of bacterial fragmentsmixed with agar that were present in higher concentrations. Results fromthree expansions with two bacterial strains indicate that the cloud dropletresiduals had virtually the same size distribution as themore » smaller particlesize mode and had mass spectra that closely matched those of bacterialfragments mixed with agar. The characterization of ice residuals that weresampled through an ice-selecting PCVI (IS-PCVI) also shows that the sameparticles that activate to form cloud droplets, bacteria fragments mixed withagar, were the only particle type observed in ice residuals. These resultsindicate that the unavoidable presence of agar or other growth media inall laboratory studies conducted on cultivated bacteria can greatlyaffect the results and needs to be considered when interpreting CCN and INactivation data.« less

Authors:

Suski, Kaitlyn J.  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-5183-7335"
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Bell, David M. ^[1]; Hiranuma, Naruki  ^[2];

• Search DOE PAGES for author "Hiranuma, Naruki"
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Möhler, Ottmar ^[2]; Imre, Dan ^[3]; Zelenyuk, Alla ^[1]

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Karlsruhe Inst. of Technology (KIT) (Germany)
3. Imre Consulting, Richland, WA (United States)

Publication Date:

2018-12-11

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1496614

Report Number(s):

PNNL-SA-131706
Journal ID: ISSN 1680-7324

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Atmospheric Chemistry and Physics (Online)

Additional Journal Information:

Journal Name: Atmospheric Chemistry and Physics (Online); Journal Volume: 18; Journal Issue: 23; Journal ID: ISSN 1680-7324

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES