Activation of Intact Bacteria and Bacterial Fragments Mixed with Agar as Cloud Droplets and Ice Crystals in Cloud Chamber Experiments

Abstract

Abstract. Biological particles, including bacteria and bacterial fragments, have been of much interest due to the special ability of some to nucleate ice at modestly low temperatures. This paper presents results from a recent study conducted on two strains of cultivated bacteria which suggest that bacterial fragments mixed with agar, and not whole bacterial cells, serve as cloud condensation nuclei (CCN). Due to the absence of whole bacteria cells in droplets, they are unable to serve as ice nucleating particles (INPs) in the immersion mode under the experimental conditions. Experiments were conducted at the Aerosol 15Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber at the Karlsruhe Institute of Technology (KIT) by injecting bacteria-containing aerosol samples into the cloud chamber and inducing cloud formation by expansion over a temperature range of -5 to -12 °C. Cloud droplets and ice crystals were sampled through a pumped counterflow virtual impactor inlet (PCVI) and their residuals were characterized with a single particle mass spectrometer (miniSPLAT). The size distribution of the overall aerosol was bimodal, with a large particle mode composed of intact bacteria and a mode of smaller particles 20 composed of agar mixed with bacterial fragments that were present in higher concentrations. Results from three expansions with two bacterial strains indicate that the cloud droplet residuals had virtually the same size distribution as the smaller particle size mode and had mass spectra that closely matched those of agar and bacterial fragments. The characterization of ice residuals that were sampled through an ice-selecting PCVI (IS-PCVI) also shows that the same particles that activate to form cloud droplets, bacteria fragments mixed with agar, were the only particle type observed in ice residuals. 25

Ice‐Nucleating Particles That Impact Clouds and Climate: Observational and Modeling Research Needs

“…Direct chemical analysis can be accomplished by nucleating immersed particles into ice crystals within a continuous flow diffusion chamber (CFDC)‐type instrument or a cloud chamber (Möhler et al., 2001) and isolating nucleated ice crystals by taking advantage of their relatively large size and inertia. Ice crystals containing INPs may be either (a) collected via impaction onto substrates for offline microscopy analysis (e.g., Kreidenweis et al., 1998, Figure 3) or (b) preferentially sampled via counterflow virtual impaction and analyzed in situ with single‐particle mass spectrometry (Cziczo et al., 2003; Hiranuma et al., 2016; Suski, Bell, et al., 2018). A similar approach can be used to analyze the residual material contained in cloud ice from for example, aircraft platforms (e.g., Cziczo et al., 2017; Noone et al., 1988; Ogren et al., 1985; Twohy et al., 1997; Zelenyuk et al., 2015).…”

“…Biological particle fragments : Recently, laboratory experiments have also shown that small fragments of biological particles (e.g., bacteria, fungal spores, and pollen) can serve as INPs (Augustin et al., 2013; Pummer et al., 2012, 2015; Suski, Bell, et al., 2018). Leaf litter has also been shown to be a potent source of INPs (Schnell & Vali, 1976).…”

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

“…Data availability. The data used in this paper are available at https: //dtn2.pnl.gov/data/release/2018_Suski_et_al_Bacteria_Paper/ (Suski, 2018).…”

Analysis of single‐cell microbial mass spectra profiles from single‐particle aerosol mass spectrometry

“…Single‐particle aerosol mass spectrometry (SPAMS) is reported to be a useful online mass spectral tool 2–4 for studying bioaerosols 5–9 . Specific marker substances such as phosphate (PO − , PO 2 − , PO 3 − ), organic nitrogen (CN − , CNO − ), 3,10–13 amino acids, and nucleotide fragments can be detected and used to recognize single‐cell microorganisms 14 …”

“…Although bioaerosol SPMS can be analyzed automatically and continuously, distinguishing among biological aerosols is still challenging 21 as few molecular markers and signatures are available for interpreting SPMS data in comparison with those produced by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) 11–13,22–24 . One reason is that the actual laser energy from each ionization instance always varies according to a Gaussian distribution 25 .…”