In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Biology

In the

School of Biological Sciences

Lizbeth Dávila Santiago

Will defend her dissertation

TOWARD QUANTIFYING THE PATTERNS OF BACTERIA AND FUNGI IN THE ATMOSPHERE AND THEIR FUNCTIONAL ROLE IN CLOUD FORMATION VIA ICE NUCLEATION

31st MARCH 2023

1:00 PM

https://gatech.zoom.us/j/93028392729

 Thesis Advisor:

Konstantinos T. Konstantinidis, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Thomas DiCristina, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Joel Kostka, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Frank Stewart, Ph.D.

Department of Microbiology and Cell Biology

Montana State University

Nga Lee, Ph.D.

School of Chemical and Biomolecular Engineering

Georgia Institute of Technology

ABSTRACT:

Bioaerosols, specifically airborne bacteria and fungi cells or cell fragments, are ubiquitous in the Earth's atmosphere and could contribute to climate and weather patterns by acting as ice nuclei (IN) for cloud formation and precipitation. However, the composition of airborne microbes and how this may change depending on the prevailing conditions in the atmosphere remain poorly understood despite their apparent importance for public health and the climate. To provide new insights into these questions, we established a time series of dry-air and rain samples, collected in an urban setting (Metro Atlanta) over two consecutive years. Amplicon sequencing of these samples revealed significant changes in microbial composition between dry-air vs. rain, including elevated abundances of pathogenic and/or allergen bacteria and fungi in dry samples, that were not driven by seasonality. Further, we assessed the effect of atmospheric conditions such as high acidic, oxidative and UV radiation stress, on the IN activity of three IN-efficient bacterial species using a newly developed chamber in collaboration in the laboratory. Our results showed that Pseudomonas syringae retained efficient IN activity (T50 above -10ºC; T50 represents the temperature that 50% of the water droplets froze as an effect of the present of the cells) even after viability loss due to acidic pH (pH = 2.5). Collectively, our findings provide new quantitative insights into the public health aspect of bioaerosols as well as their role in weather/climate patterns.