Berkeley Lab

Erica Majumder wins best overall poster at the International Symposium on Microbial Sulfur Metabolism

ENIGMA postdoc Erica Majumder’s poster “Beyond Sulfide: The Sulfur-Metabolome of Sulfate-Reducing Bacteria” affirms ENIGMA’s contribution to the ability to sulfur sulfur metabolism on a molecular level. Sulfur-containing metabolites are key to the maintenance of the redox state of the environment, the cycling of essential nutrients between microbes, the interaction of some microbes with metals and can inhibit other metabolisms such as nitrate reduction. This project developed tools to be able to assay sulfur-containing metabolites and to begin to tease out their functions in microbial community interactions.

Authors: Erica L.-W. Majumder, Tao Huan, Erica M. Forsberg, Chavi Domingo, Gary Siuzdak, Judy D. Wall
Affiliations: 1-Mizzou, 2- Scripps

A strategy to determine all sulfur-containing metabolites from global untargeted metabolomics experiments has been employed to study the total metabolome and the sulfur-ome of model Sulfate-Reducing Bacterium (SRB) Desulfovibrio vulgaris Hildenborough (DvH). Total metabolite populations were measured from DvH samples at different growth stages, on different amounts of sulfate, with competing sulfur sources, spent media, and on medium simulating the groundwater at Oak Ridge Field Research Center. The metabolome and sulfur-ome of a nitrate-reducing bacterium, a different sulfate-reducing bacterium, and E. coli were also measured using the same treatment. Using a new script we developed, the sulfur-containing metabolites were identified from the data sets. SRB were found to produce more and distinct sulfur-containing metabolites than non-sulfur respiring bacteria. For DvH, growth stage, sulfur source and sulfate concentration impacted the sulfur-ome. The biosynthesis or assimilation of these sulfur- containing metabolites was further queried with stable isotope experiments by replacing sulfate with 34 SO4 2-. DvH was found to assimilate sulfur from sulfate into certain sulfur-containing metabolites. Overall, this work indicates that the population of sulfur-containing metabolites is larger than expected, assimilative pathways are happening in dissimilatory SRB, and in addition to hydrogen sulfide, excreted sulfur-containing metabolites could be playing a role in the various environments of SRB. We have developed a new way to study sulfur metabolites in systems, which is desirable because of their reactivity and chemical properties for field and medical applications.

Relevance to ENIGMA mission 
  • Sulfur is an essential element in all kingdoms of life and the sulfur cycle is a primary driver of carbon cycling in the subsurface.
  • Many sulfur-containing metabolites are unknown or uncharacterized due to challenging chemistry.
  • Sulfur-containing molecules have increased activity/function compared to their small percent of cellular elemental composition.
  • We hypothesized that in addition to essential S-metabolites, organisms using sulfur for respiration would have a different set S-metabolites than non-sulfur respiring microbes.
  • We found that sulfur-species respiring bacteria and other respiratory-mode bacteria all had about 200 sulfur-containing metabolites using global untargeted metabolomics coupled with a new script we developed for identifying sulfur-containing metabolites.
  • We found that sulfate-reducing bacteria assimilate the sulfate sulfur and can use thiosulfate to make cysteine using stable-isotope label sulfate.
  • We also found evidence of sulfur-containing metabolites regulating protein translation and other metabolic functions.
  • Sulfur-containing metabolites in the spent medium indicate how sulfur (and carbon) may be moving between organisms or how the redox state of the environment is regulated.