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Pictured here are cells of "Ferroplasma acidarmanus" in log phase (day 7) grown in liquid culture medium mfer, in which the main constituents are sulfuric acid, yeast extract, and FeSO4.  Cells are pleomorphic, appearing in a multiple number of shapes.  Two of the shapes observed are irregular cocci (red arrows) and comma shape (yellow arrow).  Cells range in size from 0.48 to 1.08 µm long and 0.48 to 0.85 µm wide.​
In comparison to the growth of Escherichia coli in the laboratory which has a generation or doubling time of 15 to 20 minutes, "F. acidarmanus" grows much slower with a generation time of ~2 days when grown at pH 1.0.  When fresh liquid culture medium mfer (1) is inoculated with "F. acidarmanus," turbidity appears at day 5, and the cell numbers continue to increase until day 12.  The midpoint of this growth cycle is called log phase, since the cells are increasing in number in a logarithmic fashion.  ​

Methods ​

Phase-contrast microscopy is preferable to bright field microscopy when high magnifications (such as 1,000x) are required and the specimen is colorless.  Through the use of phase contrast, a reduction in brightness of the cells is achieved allowing a high-contrast image of cells to be observed.  To observe "F. acidarmanus" microscopically by phase contrast, suspensions of uninoculated mfer (pH 1.0) were applied to the surface of a glass slide with a 3% agarose pad.  Then a 7-day-old cell suspension was applied to the agarose pad followed by a cover slip and the slide was observed under 1,000x magnification on a Nikon Eclipse TE300 inverted microscope. Images were recorded electronically using a digital camera (Hamamatsu, Hamamatsu-City, Japan; model #C4742-95-10NR) and a personal computer equipped with MetaMorph software v. 4.5r6 (Universal Imaging Corporation, West Chester, PA). Using an agarose pad helps to slow the movement of cells so that you can view them more easily and take pictures.  Without the use of an agarose pad, viewing cells using the traditional wet-mount technique would be difficult as cells are moving so fast in and out of focus that taking a picture is not possible. This technique can be used with many different types of microorganisms.  To make an agarose pad, 3% (wt/vol) molecular grade agarose in sterile distilled water is microwaved to melt the agarose and then applied to the slide with a Pasteur pipette (also called an eye dropper) as a thin layer that solidifies once it cools. ​

Discussion ​
The term extremophile is derived from the Greek word "philos," meaning "to love," and the word "extreme."  Hence extremophiles are organisms that love extreme environments and have been found thriving on Earth in extreme conditions such as temperatures (-15 to 121 ° C), pH values (pH 0.0 to 12.8), hydrostatic pressures (up to 1,200 times atmospheric), high salt (up to 30% [wt/vol] NaCl), or dryness (such as a desert). Acidophiles are defined as organisms that grow optimally at pH values less than 3.0. "F. acidarmanus" was isolated from the Richmond mine in Iron Mountain, California (2), where the most acidic and metal-rich solutions as low as pH -3.7 have been reported on Earth (3).  " F. acidarmanus" grows optimally at pH 1.0 and within a pH range of 0.0 to 2.5, hence it is one of only two prokaryotic microorganisms capable of growth as low as pH 0.0 (2, 4).  The name of the organism appears in quotations, since it is not an officially approved taxonomic name according to the List of Prokaryotic names with Standing in Nomenclature found at  ​

References ​

1. Baumler, D. J., K. C. Jeong, B. G. Fox, J. F. Banfield, and C. W. Kaspar. 2005. Sulfate requirement for heterotrophic growth of "Ferroplasma acidarmanus" strain fer1. Res. Microbiol. 156:492–498. ​

2. Edwards, K. J., P. L. Bond, T. M. Gihring, and J. F. Banfield. 2000. An archaeal iron-oxidizing extreme acidophile important in acid mine drainage. Science 287:1796–1799. ​

3. Nordstrom, D. K., and C. N. Alpers. 1999. Negative pH, efflorescent mineralogy, and consequences for environmental restoration at the iron mountain superfund site, California. Proc. Natl. Acad. Sci. USA 96(7):3455–3462. ​

4. Schleper, C., G. Puehler, I. Holz, A. Gambacorta, D. Janekovic, U. Santarius, H. -P. Klenk, and W. Zillig. 1995. Picrophilusgen. Nov., Fam. nov.: a novel aerobic, heterotrophic, thermoacidophilic genus and family comprising Archaea capable of growth around pH 0.  J. Bacteriol. 177:7050–7059. ​

​Slide 3: Ferroplasma acidarmanus (Enlarged view)​

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