Recent studies have suggested that live bacteria in cloudwater can play important roles in affecting the formation of aqueous-phase secondary organic aerosols (SOA) via the biological degradation of organic compounds such as organic acids. However, clouds are known to be harsh environments for live bacteria because they are exposed to a variety of atmospheric conditions (e.g., solar radiation, high acidity) that are considered to be harmful to bacteria cells. Here, we will present results on how direct photolysis impacts the survival rates and metabolism of two non-sporing bacteria species (Pseudomonas and Bacillus) and one sporing bacteria species (Bacillus) under cloudwater-like conditions. These three species are among the most represented in cultivable community in atmospheric clouds. We observed that photolysis strongly negatively affected the survival and energetic metabolism of all bacteria strains under highly acidic conditions (pH ~3) but had little impact on the survival and energetic metabolism of bacteria under mildly acidic conditions (pH ~5). In addition, we found that various organic compounds such as constituents of cell membrane and metabolites were produced by the non-sporing bacteria strains during different stages of photolysis. These organic compounds can potentially contribute to aqueous SOA formation. Next, we will present results on how light and acidity impact the abilities of Pseudomonas and Bacillus bacteria to biodegrade a variety of organic acids that are commonly detected in cloudwater. Noticeable faster biodegradation rates for some organic acids (formic and oxalic acids) were observed under dark and mildly acidic (~pH 5) conditions. Overall, these results highlight the different mechanisms by which live bacteria can influence SOA formation in atmospheric cloudwater.

Photolytical aging of live bacteria under cloud-like conditions and its impact on aqueous secondary organic aerosol formation

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.