Related Experiment Video
Updated: Aug 4, 2026
09:31
Preparation of Authigenic Pyrite from Methane-bearing Sediments for In Situ Sulfur Isotope Analysis Using SIMS
Published on: August 31, 2017
Stable carbon isotope fractionation by sulfate-reducing bacteria
Kathleen L Londry1, David J Des Marais
1Exobiology Branch, NASA Ames Research Center, Moffett Field, California, USA. londryk@umanitoba.ca
Applied and Environmental Microbiology
|May 7, 2003
Summary
Sulfate-reducing bacteria (SRB) show varied carbon isotope discrimination during growth. This discrimination is influenced by metabolic pathways and environmental conditions, impacting the fossil record.
Area of Science:
- Biogeochemistry
- Microbiology
- Isotope Geochemistry
Background:
- Anoxic sedimentary environments host microbial communities that influence geochemical signatures.
- Sulfate-reducing bacteria (SRB) play a key role in biogeochemical cycling in these environments.
- Understanding carbon isotope fractionation by SRB is crucial for interpreting the fossil record.
Purpose of the Study:
- To determine carbon isotope discrimination associated with heterotrophic and lithotrophic growth of SRB.
- To investigate how metabolic pathways and growth conditions affect carbon isotope fractionation in SRB.
- To assess the implications of SRB carbon isotope discrimination for paleoclimate and paleoenvironmental reconstructions.
Main Methods:
- Culturing of pure SRB strains under controlled heterotrophic, lithotrophic, and mixotrophic conditions.
- Monitoring of substrate consumption and biomass production.
- Determination of delta(13)C values for substrates, CO(2), and biomass using isotope ratio mass spectrometry.
Main Results:
- Most SRB exhibited small carbon isotope effects (0–2‰) between substrates and biomass during heterotrophic growth.
- Desulfotomaculum acetoxidans showed a significant enrichment of 13C in biomass (8–9‰) compared to substrates.
- Lithotrophic growth resulted in substantial carbon isotope fractionation, with values varying among species (e.g., Desulfotomaculum acetoxidans: 1.0310).
- Mixotrophic growth yielded biomass with intermediate delta(13)C values.
- Fractionation extent depended on enzymatic pathways, direction of operation, and growth rate, but not growth phase.
Conclusions:
- Carbon isotope discrimination by SRB is species-specific and condition-dependent.
- SRB metabolism significantly influences the carbon isotopic signatures preserved in sedimentary organic matter.
- Ecological factors affecting substrate and reductant availability can modulate carbon isotope discrimination by SRB in natural environments.
More Related Videos
Related Concept Videos
01:22The Sulfur Cycle
Sulfur, an important element in the chemical makeup of proteins, is recycled through the atmosphere and aquatic and terrestrial environments. Found in the atmosphere as sulfur dioxide (SO2), sulfur is released by decaying organisms, weathered rocks, geothermal vents, volcanos, and burning fossil fuels. It is deposited into the ecosystem, cycled through the biotic community, and either released back into the atmosphere as gas or deposited in marine sediment for long-term storage and eventual...
01:28Carbon-dioxide Fixation
Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...
01:20Sulfur Assimilation
Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to become...
01:24Microbes and the Carbon Cycle
The carbon cycle is a fundamental Earth process involving the transfer of carbon among the biosphere, lithosphere, atmosphere, and hydrosphere. It plays a critical role in regulating the planet’s climate and supporting life by cycling carbon through various chemical forms and reservoirs. Carbon primarily circulates as carbon dioxide (CO₂), representing its oxidized form, while reduced forms such as methane (CH₄) and organic compounds also play essential roles.Microbial activity is central to...
01:29Microbes and the Sulfur Cycle
Sulfur is a vital element in Earth's biogeochemical systems. It transitions through various inorganic states, including sulfate (SO₄²⁻), elemental sulfur (S⁰), and sulfide (S²⁻). Abiotic and biological mechanisms across oxic and anoxic environments intricately mediate these transformations. Sulfate, the most oxidized form of sulfur, is predominantly stored in rocks, marine sediments, and oceanic waters, acting as a long-term reservoir in the global sulfur cycle.In oxic environments,...
01:24Microbes and Other Elemental Cycles
Microbial activity plays a pivotal role in the biogeochemical cycling of iron and manganese, especially at the redox gradients characteristic of stratified aquatic environments. These cycles are driven by microbial transformations between oxidized and reduced forms of the metals, allowing organisms to exploit them for metabolic energy and structural purposes.Iron Cycling Across Redox GradientsIn neutral, oxygen-rich surface waters, iron is predominantly found in its oxidized, insoluble ferric...