8.15E: Archaeoglobus

Archaeoglobus is a genus of Euryarchaeota found in high-temperature oil fields.

Learning Objectives

• Outline the unique traits associated with Archaeoglobus

Key Points

• Archaeoglobus are sulfate-reducing archaea, coupling the reduction of sulfate to sulfide with the oxidation of many different organic carbon sources, including complex polymers.
• Archaeoglobus grow at extremely high temperatures and are found in hydrothermal vents, oil deposits, and hot springs.
• Comparative genomic studies on archaeal genomes provide evidence that members of the genus Archaeoglobus are the closest relatives of methanogenic archaea.

Key Terms

• lithoautotroph: A microbe that takes energy from reduced compounds of minerals.
• heterotroph: An organism that requires an external supply of energy in the form of food as it cannot synthesize its own.
• hyperthermophiles: An organism that thrives in extremely hot environments-from 60 degrees C (140 degrees F) upwards.

Archaeoglobus is a genus of Euryarchaeota found in high-temperature oil fields, where they may contribute to oil field souring. Archaeoglobus are sulfate-reducing archaea, coupling the reduction of sulfate to sulfide with the oxidation of many different organic carbon sources, including complex polymers.

Archaeoglobus grow at extremely high temperatures between 60 and 95 °C, with optimal growth at 83 °C. These hyperthermophiles can be found in hydrothermal vents, oil deposits, and hot springs. They can produce biofilm to form a protective environment when subjected to environmental stresses such as extreme pH or temperature, high concentrations of metal, or the addition of antibiotics, xenobiotics, or oxygen. These archaeons are known to cause the corrosion of iron and steel in oil and gas processing systems by producing iron sulphide. Their bioflims, however, may have industrial or research applications in the detoxification of metal contaminated samples or to gather metals in an economically recoverable form.

Figure: Microbial Mats Around the Grand Prismatic Spring: Thermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park

Archaeoglobus are lithotrophs, and can be either autotrophic or heterotrophic.The archaeoglobus strain A. lithotrophicus are lithoautotrophs, and derive their energy from hydrogen, sulfate and carbon dioxide. The strain A. profundus are also lithotrophic, but as they require acetate and CO2 for biosynthesis, and are therefore heterotrophs. Archaeoglobus species utilize their environment by acting as scavengers with many potential carbon sources. They can obtain carbon from fatty acids, the degradation of amino acids, aldehydes, organic acids, and possibly carbon monoxide (CO) as well.

Comparative genomic studies on archaeal genomes provide evidence that members of the genus Archaeoglobus are the closest relatives of methanogenic archaea. This is supported by the presence of 10 conserved signature proteins that are uniquely found in all methanogens and Archaeoglobus. Additionally, 18 proteins which are uniquely found in members of Thermococci, Archaeoglobus and methanogens have been identified, suggesting that these three groups of Archaea may have shared a common relative exclusive of other Archaea. However, the possibility that the shared presence of these signature proteins in these archaeal lineages is due to lateral gene transfer cannot be excluded.

The complete genome sequence from Archaeoglobus fulgidus reveals the presence of a complete set of genes for methanogenesis. The function of these genes in A. fulgidus remains unknown, and the lack of the enzyme methyl-CoM reductase does not allow for methanogenesis to occur by a mechanism similar to that found in other methanogens.

The A. fulgidus genome is a circular chromosome of 2,178,000 base pairs, roughly half the size of E. coli. A quarter of the genome encodes preserved proteins whose functions are not yet determined, but are expressed in other archaeons such as Methanococcus jannaschii. Another quarter encodes proteins unique to the archaeal domain. One observation about the genome is that there are many gene duplications and the duplicated proteins are not identical. This suggests metabolic differentiation specifically with respect to the decomposing and recycling carbon pathways through scavenged fatty acids. The duplicated genes also gives the genome a larger genome size than its fellow archaeon M. jannaschii.