Figure 1.  An electron micrograph of Ferroplasma acidarmanus.

Discovered in 1997 by Dr. Katrina J. Edwards et al. as a Ph.D. project, Ferroplasma acidarmanus is an extreme acidophile that lives in the most acidic conditions on earth (1).  This astonishing microbe, upon examination of various factors within its environment, flourishes in a place that should be more aptly named hell on earth rather than an abandoned mine.
 

In her paper, An Archaeal Iron-Oxidizing Extreme Acidophile Important in Acid Mine Drainage, Edwards et al. describes the location within Iron Mountain where she isolated the chemomixotrophic archaeon during her research of microbes that live in various locations inside the mine.  In addition, she describes procedures used to identify the isolate, such as comparisons of DNA, habitat, and growth requirements with those of other organisms within the Ferroplasma genera (2).  They determined the isolate was a new species within the phylum Euryarchaeota; class Thermoplasmata; order Thermoplasmatales, and family Ferroplasmaceae, as Ferroplasma acidarmanus (3).  It was discovered that F. acidarmanus preferentially grows on pyrite (FeS₂), instead of organic media.  Edwards also determined the archaeon plays a significant roll in the production of Acid Mine Drainage (AMD) due to its abilities to regenerate     Fe³⁺, a pyrite oxidizer (2).

Iron Mountain is an abandoned mine encasing a large tunnel system and several AMD streams that run through a sulfide ore body and into the Sacramento River (4).  Located in Redding, California and exhibiting the most inhospitable conditions recorded to date, it is the only known home to Ferroplasma acidarmanus.  Temperatures range from 15-50°C, with internal stream pH values of 3.5 or less depending on the location within the mine shaft (4).  The stream Edwards collected isolates from is found approximately 500m inside the mine at a location known as the Richmond 5-way, housing 5 intersecting tunnels (2).  The stream is roughly 1m across and is filled with a thick biofilm  found in most of the subsurface streams.  These waters  contain high concentrations of sulfuric acid, copper, arsenic, cadmium, and zinc; a mixture usually lethal to most other organisms (5).  F. acidarmanus is a seasonal microbe, the dense slime streamers it creates can only be witnessed during the summer and fall months at the Richmond 5-way (2).

Figure 3.  A map showing the location of Iron Mountain.

Figure 4.  An Acid Mine Drainage stream at Iron Mountain.

Figure 5. The slime streamers found at the Richmond 5-way.

Characteristic of many archaeons, F. acidarmanus does not have a cell wall, only a single cell membrane (5).  It thrives in the acidic waters of the Richmond 5-way, living at a pH between 0 and 2.5, and prefers to grow attached to mineral surfaces instead of free floating in solution.  With an optimal pH of 1.2, it can not survive in neutral pH water as it will readily lyse, making its acidic environment essential (2).  After reviewing the incredible conditions in which Ferroplasma acidarmanus thrives, one could refer to this microbe as the devil of the microbes surviving in a living hell.

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