Fossil Fuel Bioprocessing projects
Microbial Chlorate Reduction as a Control of Biogenic Hydrogen Sulfide Production in Oil Reservoirs
The generation of hydrogen sulfide (H2S) as a metabolic end product of microbial sulfate respiration results in a variety of oil recovery problems, including oil reservoir souring, contamination of crude oil, and metal corrosion. It may be possible to control the generation of biogenic H2S through the activity of sulfur-oxidizing bacteria. This project is determining the ability of chlorate-reducing bacteria to inhibit and reverse microbial sulfate reduction, to identify the environmental and biological parameters under which this occurs, and to demonstrate that suitable chlorate-reducing populations are indigenous to oil reservoirs.
H2S biogenesis results in reservoir souring, metal corrosion, metal-sulfide precipitation, and toxicity to field personnel. Sour service metallurgy carries an estimated premium of 2% of total costs at project initiation but may be tenfold higher if retrofitted.
Traditionally, nitrate addition is used to inhibit sulfidogenesis. However, the perceived inhibitory mechanism is controversial with a resulting unpredictability in its efficacy. We investigated an alternative souring control, taking advantage of dissimilatory (per)chlorate-reducing bacteria (DPRB) metabolism. We demonstrated that these thermodynamically favorable organisms preferentially couple H2S oxidation to (per)chlorate (ClO4-, ClO3-) reduction. In contrast to known sulfur oxidizers, sulfur oxyanions are not produced and elemental sulfur (So) is precipitated, allowing easy separation. Microcosm, packed-column, and pure culture studies amended with DPRB and (per)chlorate all demonstrated sulfidogenesis inhibition and sulfide removal. Although conceivable, significant microbial So re-reduction to H2S in-situ is unlikely as the metabolism is less favorable than methanogenesis, suggesting that methane production would dominate. Furthermore, we demonstrated that chlorine oxyanions are specifically toxic to sulfate reducing bacteria (SRB), putatively inhibiting the ATP-sulfurylase, a requisite enzyme conserved amongst SRB, preventing further sulfidogenesis.
These studies identify a unique, effective alternative to souring control and reveal some conceptual fallacies surrounding nitrate application. Furthermore, because of similar physical-chemical properties and commercial cost, the application of (per)chlorate is competitive with that of nitrate, making an easy exchange of one technology for the other.
Coates’ team isolated, characterized and sequenced the genomes of two novel perchlorate-reducing bacteria from marine sediments and Athabasca River samples. Researchers also collected other samples from a diverse range of environments. They identified the putative pathway involved in H2S oxidation, and investigated environmental parameters that control H2S oxidation.
Published in 2012
Draft Genome Sequence of the Anaerobic, Nitrate-Dependent, Fe(II)-Oxidizing Bacterium Pseudogulbenkiania ferrooxidans Strain 2002 , Kathryne Byrne-Bailey, Karrie Weber, John D. Coates, Journal of Bacteriology, 194(9), pp. 2400-2401, doi: 10.1128/JB.00214-12, May 2012.
Bioelectrical Redox Cycling of Anthraquinone-2,6-Disulfonate Coupled to Perchlorate Reduction, Iain Clark, Hans Carlson, Anthony Iavarone, John D. Coates, Energy & Environmental Science, doi: 10.1039/c0xx00000x, Accepted Manuscript, May 2012.
Towards a Mechanistic Understanding of Anaerobic Nitrate Dependent Iron Oxidation: Balancing Electron Uptake and Detoxification, Hans Karl Carlson, Iain Clark, Ryan Melnyk, John D. Coates, Frontiers in Microbiology, 3:57, doi: 10.3389/fmicb.2012.00057, February 20, 2012.
Surface Multiheme C-Type Cytochromes from Thermincola potens and Implications for Dissimilatory Metal Reduction by Gram-Positive Bacteria, Hans Carlson, Anthony Iavarone, Amita Gorur, Boon Siang Yeo, Rosalie Tran, Ryan Melnyk, Richard Mathies, Manfred Auer, John D. Coates, Proceedings of the National Academy of Sciences, 109(5), pp. 1702-1707, doi: 10.1073/pnas.1112905109, January 31, 2012.
Published in 2011
Identification of a Perchlorate Reduction Genomic Island with Novel Regulatory and Metabolic Genes, Ryan Melnyk, Anna Engelbrektson, Iain Clark, Hans Carlson, Kathy Byrne-Bailey, John D. Coates, Applied and Environmental Microbiology, doi: 10.1128/AEM.05758-11, August 2011.