Sulfur Metabolites in the North Pacific Subtropical Gyre and Transition Zone

Abstract

Sulfur is an essential nutrient for life and a constituent of many important biomolecules. Phytoplankton in the surface ocean use assimilatory reduction pathways to reduce inorganic sulfur, primarily in the form of sulfate (SO4 2-), into the necessary organic compounds. Many marine microbes including Pelagibacter, the most abundant and ubiquitous heterotrophic bacteria, do not have these pathways and are not able to reduce their own sulfur. These organisms therefore require exogenous sources of reduced sulfur. While some sulfur compounds, such as DMSP or DHPS, have been well studied, the entire composition of sulfur and the roles of these compounds is poorly understood. Metabolomics were used to characterize the composition of sulfur metabolites from four particulate depth profiles in the North Pacific. This study quantified 12 sulfur metabolites within particulate matter of the North Pacific. I identified gonyol as the most abundant of these sulfur metabolites. This sulfonium likely plays an important role in sulfur cycling as a source of reduced sulfur for the heterotrophic bacteria. Sulfonates, the more oxidized form of sulfur, likely play a key role in communities north of the North Pacific Transition Zone as they are the most abundant form of sulfur in this area. This research highlights the importance of these understudied compounds and provides a foundation for future research on sulfur cycling in the marine environment.