UC Santa Cruz

Atmospheric aerosols (suspension of solid or liquid particles in the present in the atmosphere) can harbor a diverse array of airborne microorganisms and upon deposition into terrestrial or marine systems, airborne microbes can alter function and biogeochemical cycles of the receiving ecosystems. My work focuses on aerosols and their impact on marine environments. The three chapters in this thesis examine 1) the abundance and diversity of airborne microorganisms over the Mediterranean Sea, 2) the impacts of airborne microorganisms on the northern Red Sea surface water microbial diversity and function, and 3) the efficiency of three types of aerosol sampling instrumentation. In the first study, I described the abundance and genetic diversity of airborne bacteria in air samples collected over an East-West transect of the entire Mediterranean Sea and investigated 1) the controls on the diversity of airborne microbes, and 2) the source of the microbes comprising the aerosol microbiome over the Mediterranean Sea. The results show that airborne bacteria represent diverse groups with the most abundant bacteria from the Firmicutes (Bacilli and Clostridia) and Proteobacteria (Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria) phyla. Most of the bacteria in the samples have previously been observed in the air at other open ocean locations, in the air over the Mediterranean Sea during dust storms, and in surface water of the Mediterranean Sea. The results demonstrate that airborne bacterial diversity is positively correlated with the mineral dust content in the aerosols and the taxonomic composition differed between major basins of the Mediterranean Sea. In the second study, a mesocosm experiment was conducted to elucidate 1) how bioaerosols collected during dust-events impact prokaryotic and eukaryotic relative abundance in the northern Red Sea (NRS) surface water, and 2) how the changes in community structure affect biogeochemical cycles of the NRS. Results show that the airborne microorganisms and viruses suppressed primary production (as much as 50%), increased bacterial production (as much as 55%), and decreased the diversity of eukaryotes. These results suggest that airborne microorganisms have implications for the carbon cycle in low nutrient low chlorophyll marine ecosystems. The final chapter tests the efficiency of samples collected with three instruments (a membrane filtration device, a liquid impinger, and a portable electrostatic precipitator bioaerosol collector) for culture-dependent (colony-forming units) and culture-independent (DNA yield) studies. The results show that the electrostatic precipitator collected microorganisms significantly more efficiently than the membrane filtration and liquid impingement in both types of studies over the same time interval, primarily due to its higher flowrate.