UC San Diego

The globe is primarily made up of the Earth’s oceans, which contribute biological, chemical, and physical influences towards global environments. However, many of the marine biological impacts, specifically on the chemistry of the atmosphere, are not well understood. Compounds like Dimethylsulfoniopropionate (DMSP), and its derivative Dimethyl Sulfide (DMS), cycle through the marine environment as an exchange of carbon and sulfur among many organisms. DMSP derived DMS is also a major contributor towards irradiation of UV light and nucleation of clouds. Understanding the relationship between DMSP cycling and DMS production allows insight into biological impacts on climate.This thesis addresses how heterotrophic bacteria in the marine environment degrade the organosulfur compound DMSP and produce sulfur containing VOCs. During SeaSCAPE 2019, an induced phytoplankton bloom resulted in an increased production of dissolved DMSP (DMSPd), leading to bacterial transcription of genes coding for the enzyme which cleaves DMSP into the volatile DMS. Following, an increase in dissolved DMS was measured in the wave flume. A mesocosm experiment was conducted to investigate the metabolic pathways and showed novel insights into simultaneous degradation of DMSP into DMS and MeSH by a model organism, the Rhodobacteraceae Phaeobacter sp. La5. From our findings, heterotrophic bacteria influence the formation of DMS through enzymatic cleavage of phytoplankton produced DMSP when bacterial sulfur demand is met with excess sulfur. With these novel findings, continued research on the DMSP cleavage pathway, the genes homologs, their rates of transcription and translation, and enzyme efficiency under varying environmental conditions will better our understanding of how microbes affect the composition of the atmosphere through sulfur cycling.