Marine Bacteria Affect Saccharide Enrichment in Sea Spray Aerosol during a Phytoplankton Bloom

Saccharides are a large class of organic matter in sea spray aerosol (SSA) that can impact its climate-relevant properties. In seawater, saccharides are produced, exuded, and consumed by phytoplankton and heterotrophic bacteria (HB). Herein, we add the HB strains Alteromonas sp. (AItSIO), Pseudoalteromonas (ATVV7), and Flavobacteria bacterium (BBFL7) to marine microcosms during phytoplankton blooms and directly probe the impact of HB on the composition and size of saccharides in seawater and SSA for the first time. Enrichment factors (EFs) for saccharide SSA relative to seawater were composition- and size-dependent, ranging from 100 to 930 000 in sub-micrometer SSA and from 38 to 3700 in super-micrometer SSA. For saccharides in two similar phytoplankton blooms, lower seawater concentrations coincided with higher EFs, which may explain high saccharide enrichments in remote marine locations. Increased enzyme activity within a day of HB addition corresponded to increases in saccharide EFs in sub-micrometer SSA, by a factor of 30 for the energy-storage saccharide glucose and by a factor of 2 for the structural saccharide xylose. Meanwhile, arabinose, released in response to microorganism stress, increased by a factor of 20 in super-micrometer SSA after a lag of 2 days. Observations of HB in SSA indicate that modifications to the saccharide pool in terms of composition and size occur in both seawater and SSA, which subsequently impact their enrichment in SSA. A better understanding the chemical, biological, and physical factors that contribute to the large enrichment of saccharides in SSA will advance our ability to predict SSA composition and its impact on Earth's climate.