Extremely Thermoacidophilic Archaea in Biomining Operations: Development of Functional Genomics Tools and Methodologies

With increasing demand and decreasing supplies of base and precious metals (i.e., copper and gold), the study of bioleaching microorganisms is of great interest to the mining industry for recovery of product from low grade ores. These organisms derive energy from the reduced iron and sulfur compounds (i.e. pyrite, chalcopyrite) present as impurities. While mobilization of these impurities is a chemical process, bioleaching microorganisms capable of iron oxidation regenerate ferric ions, thus provided a catalytic boost to abiotic reaction rates. Understanding the mechanisms for iron and sulfur oxidation, as well as other factors important to the survival of bioleachers in a harsh biomining environment (CO2 fixation, metal tolerance, adhesion, etc.), is necessary to optimize biocatalyst performance and product recovery.

Metallosphaera sedula is the first extremely thermoacidophilic bioleacher to have its complete genome sequenced. Using the sequence, physiological features of importance to biomining can be studied via transcriptional analyses. To this end, a whole genome oligonucleotide microarray has been constructed for M. sedula. Culturing methodologies have been developed to ensure extraction of M. sedula mRNA representing bioleaching conditions, utilizing epifluorescent cell counts and an o-phenanthroline colorimetric assay. Initial results indicate that optimum mRNA sampling time for M. sedula occurs after the third media replacement and an additional 160 hours of growth. Additionally, preliminary efforts have been made to develop a better defined heterotrophic medium for comparison against autotrophic media containing metal sulfide substrates. Finally, evidence that transcriptional response experiments can be carried out successfully in spite of the extreme cultivation conditions is presented.