Berkeley Lab

New Pathway for Decomposition of Dissolved Organic Matter

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Schematic shows how Iron (Fe) can start a catalytic pathway that accelerates the oxidation of natural organic matter by oxygen (O2). The important reactive oxygen species intermediates are also show, hydrogen peroxide (H2O2) and superoxide (O2-●)

Scientific Achievement

We were able to experimentally demonstrate and numerically model a new pathway by which natural organic matter can be oxidized (decomposed) by oxygen. We showed that a type of organic matter that was not directly oxidized by oxygen rapidly oxidized with the addition of catalytic amounts of iron.

Significance and Impact

The pathways and rates of oxidation of natural organic matter is an important part of the global carbon cycle. If modeling of global carbon cycling is to be accurate it is important that we have a clear understanding of all the significant pathways. This work contributes to that need.

Research Details
  • We used a model organic compound to represent natural organic matter.
  • We measured the rate of oxidation of this compound in the presence and absence of iron.
  • We used a numerical kinetic model to show that iron initiates an important catalytic oxidation pathway that relies on important reactive oxygen species intermediates, hydrogen peroxide (H2O2) and superoxide (O2-●)
Citation

Yuan, X.; Davis, J. A.; Nico, P. S. (2016), Iron-Mediated Oxidation of Methoxyhydroquinone under Dark Conditions: Kinetic and Mechanistic Insights, Environmental Science & Technology, 50(4), 1731-1740 DOI: 10.1021/acs.est.5b03939.

Critical biogeochemical functions in the subsurface are associated with bacteria from new phyla and little studied lineages

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Overview of sediment microbial community composition. Colored boxes indicate curated genomes

Scientific Achievement

New methods were used to reconstruct genomes from sediments and evaluate interlinked roles in biogeochemical cycling. Community proteomics confirmed these activities. The 8 most abundant organisms belong to novel lineages, and two represent phyla with no previously sequenced genomes.

Significance and Impact

Nitrogen, sulfur and carbon fluxes in the terrestrial subsurface are mediated by microbial communities but the details are unclear. We showed that little known and newly described groups of microorganisms play central roles in these cycles.

Research Details
  • Sediments were sampled, DNA extracted and sequenced
  • New methods to recover genomes from highly complex sediment microbial communities were developed
  • Metabolic predictions were made for the eight most abundant organisms. Handoffs were uncovered
  • Organisms were classified phylogenetically and shown to derive from little known or unknown phyla
Citation

Hug, L. A.; Thomas, B. C.; Sharon, I.; Brown, C. T.; Sharma, R.; Hettich, R. L.; Wilkins, M. J.; Williams, K. H.; Singh, A.; Banfield, J. F. (2016) Critical biogeochemical functions in the subsurface are associated with bacteria from new phyla and little studied lineages, Environmental Microbiology, 18(1), 159-173 DOI: 10.1111/1462-2920.12930.

Iron and Carbon Dynamics during Aging and Reductive Transformation of Biogenic Ferrihydrite

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Scientific Achievement

Increased our understanding of the processes that control the formation of complexes between organic matter and minerals. These complexs are important for preserving organic matter so their formation pathway are an important pat of understanding carbon cycling

Significance and Impact

The results tat redox cycling of subsurface conditions creates a pathway for microbially produced organic matter to become sequestered by association with minerals is a novel observation that needs to be considered when trying to understand the carbon cycle

Research Details
  • Use DOE natural field laboratory at Rifle, CO
  • Followed changes in Fe mineralization and carbon chemistry over multiple months as redox conditions in the system cycled,.
  • Used advanced synchrotron based spectromicroscopic techniques to characterize the observed changes over time,
  • Developed a conceptual model that supports that data and improves our understanding of the system.
Citation

Cismasu, A. C.; Williams, K. H.; Nico, P. S. (2016), Iron and Carbon Dynamics during Aging and Reductive Transformation of Biogenic Ferrihydrite, Environmental Science & Technology, 50(1), 25-35, DOI: 10.1021/acs.est.5b03021.