Abstract
The ability of microorganisms to thrive under oxygen-free conditions in subsurface environments relies on the enzymatic reduction of oxidized elements, such as sulfate, ferric iron, or CO2, coupled to the oxidation of inorganic or organic compounds. A broad phylogenetic and functional diversity of microorganisms from subsurface environments has been described using isolation-based and advanced molecular ecological techniques. The physiological groups reviewed here comprise iron-, manganese-, and nitrate-reducing microorganisms. In the context of recent findings also the potential of chlorate and perchlorate [jointly termed (per)chlorate] reduction in oil reservoirs will be discussed. Special attention is given to elevated temperatures that are predominant in the deep subsurface. Microbial reduction of (per)chlorate is a thermodynamically favorable redox process, also at high temperature. However, knowledge about (per)chlorate reduction at elevated temperatures is still scarce and restricted to members of the Firmicutes and the archaeon Archaeoglobus fulgidus. By analyzing the diversity and phylogenetic distribution of functional genes in (meta)genome databases and combining this knowledge with extrapolations to earlier-made physiological observations we speculate on the potential of (per)chlorate reduction in the subsurface and more precisely oil fields. In addition, the application of (per)chlorate for bioremediation, souring control, and microbial enhanced oil recovery are addressed.
Highlights
Microorganisms inhabit subsurface environments 100s of meters below Earth’s surface where oxygen is most often lacking
The detrimental effects associated with the formation of hydrogen sulfide increase the production and refinery costs of petroleum (Tang et al, 2009) and have created a generally negative image of microorganisms in oil fields from the beginning of modern oil recovery (Bastin et al, 1926)
Growing effort is spent on the development of new strategies for microbial enhanced oil recovery (MEOR), or other processes that use the “help of microorganisms” for increasing hydrocarbon recovery
Summary
Microorganisms inhabit subsurface environments 100s of meters below Earth’s surface where oxygen is most often lacking. A limited number of strains with the ability to reduce soluble and insoluble forms of ferric iron [e.g., Shewanella putrefaciens (formerly named Alteromonas putrefaciens)] was isolated from oil reservoirs (Semple and Westlake, 1987; Semple et al, 1989).
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