Ferroplasma acidarmanus
Jaime Statler

Ferroplasma acidarmanus was discovered in the late 1990s by Katrina Edwards and her team from the University of Wisconsin – Madison, with the discovery published in 2000. The group was studying microbial populations in acid mine drainage in Iron Mountain, California when they found a hardier, more resilient relative of the F. acidophilus species. The organism falls into the order Thermoplasmales, which is characterized by the lack of a cell wall in the representative species. The only barrier this cell has from its preferred environment of highly acidic and metal-rich water is a single membrane. In the Iron Mountain drainage in which F. acidarmanus was discovered, the temperature sits at around 40 C and the pH at 0 to 1, with qualities essentially similar to battery acid. The species is capable of growing at pH 0-2.5, with an optimum growth pH of 1.2. At optimum pH, it doubles its population in 32 hours. In comparison, its brother, F. acidophilus, grows at pH 1.3 to 2.2, with an optimum pH of 1.7, and a doubling time three times longer than F. acidarmanus. Only two other organisms are known that are capable of surviving at pH 0, the lowest pH known to support life.

One of the wonders of this archaean is the fact that it survives in the extremely harsh environment of mine water runoff, yet has no cell wall. The cell is believed to keep its cytoplasmic pH at near-neutral through the structure of its cell membrane, which prevents the diffusion of protons into the cytoplasm. Additionally, this microbe thrives in extremely high concentrations of metals (not to mention the heat), with iron concentrations over 100 g/L, and copper, arsenic, zinc, and cadmium ranging up to tens of grams per liter. One study showed the organism capable of growing in copper concentrations up to 20 g/L.

F. acidarmanus appears to contribute greatly to acid mine drainage, responsible for billions of dollars in environmental damage. In some sites, it comprises over 85% of the microbe population in runoff from Iron Mountain. It grows preferentially on exposed pyrite surfaces, oxidizing the iron and sulfide to release sulfuric acid and insoluble ferric ions. The environment created by mining industries, exposing metals to air and water, essentially creates a eutrophic environment which allows extremophiles to thrive, accelerating the natural processes of iron and sulfur cycling. It is believed that microbes such as F. acidarmanus play important roles in global iron and sulfur cycling.

The genome of the species has recently been sequenced, which hopefully will open doors into understanding how it is capable of thriving in conditions which would kill the majority of organisms. It lacks the major mode of protection used by almost all other prokaryotes, the cell wall, yet lives in more extreme environments than any other organism. It is a puzzling and tough little bug which scientists hope will provide clues to the origins of life on Earth, as well as the chance that life exists beyond Earth.







*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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