There is a hot little microbe called Ignicoccus hospitalis (“the friendly fire sphere”) who lives in the turbulent, oxygen-free, hydrothermal vents in the North of Iceland; conditions very much like those on ancient Earth. But it doesn’t live alone.
l. hospitalis, as it’s affectionately known to the microbiology crowd, has a committed relationship with an even smaller microbe, Nanoarchaeum equitans (“The riding dwarf”) which has the puniest genome known and, without the genes to do very much itself, depends entirely on I. hospitalis for just about everything it needs. Much is being learned about this microbial odd couple because both thrive in temperatures up to 100oCentigrade in Harald Huber’s oxygen-free, sulfur-rich biotope at the University of Regensburg in Germany.
Archaea Are Among the Most Ancient Life Forms on Earth
Ignicoccus hospitalis and N. equitans are both Archaea, a group that includes many heat-loving microorganisms and likely descended from the first living creatures on our world; in fact, Dr. Huber thinks that N. equitans is a particularly primitive life form, possibly even a living fossil, around from the very beginning of life on Earth. Archaeons, named after the Archaean era which began about 3,800 to 2,500 million years ago, are ancient microbes with the extreme survival skills.
And Then There Are Bacteria and Eukaryota
The other two life forms or “domains,” according to evolutionary biologists, are Bacteria and Eukaryotes. Archaea and Bacteria, although very different, are often lumped together as “Prokaryotes;” making some scientists extremely unhappy. Norman R. Pace from the University of Colorado in Boulder, for example, says “the prokaryote notion distorts and misleads,” because the three domains Bacteria, Archaea and Eukaryota are distinct forms of life evolving from a Last Universal Common Ancestor (LUCA). The term prokaryote is outdated, Pace stresses, left over from a time when people thought all tiny microbes were bacteria. In the 1970s Carl Woese at the University of Illinois at Urbana-Champaign changed all that when he and his colleagues discovered that a group of bizarre microbes were fundamentally different than Bacteria and named them Archaea.
James A Lake from the University of California in Los Angeles has a slightly different slant on the matter. He and a number of other researchers including Martin Embley from Newcastle University in the UK, say new biochemical data support the “eocyte hypothesis” which acknowledges a eubacterial LUCA but holds that Archaea evolved from it and Eukaryotes arose from a branch of the Archaea: the Eocytes, which is another name for Crenarchaeota and that brings us back to I. hospitalis which is quintessentially crenarchaeal.
And Now for the Big Surprise – I. hospitalis Has an Energized Outer Membrane
Dr. Huber and his scientific team led by Ulf Küper recently discovered that unlike any other Archaea or Bacteria, and a goodly number of each are known; I. hospitalis keeps its energy-making apparatus in an outer membrane and produces the energy in its periplasm. “Granted, this is the hyperthermophile who helped shatter the ancient belief that life at high temperatures is not plossible, thus hardly a conformist,” says Moselio Schaechter from the University of California at San Diego. “But this most recent discovery is, to say the least, unexpected.”
The energetic business-end of both archaeons and Bacteria is usually the membrane closest to the microbe’s information processing and protein biosynthesis, or the “cytoplasmic membrane.” Both processes demand a lot of energy and making it right where the action is works well for most microbes.
An I. hospitalis – Like Archaeon May have been Ancestor to a Eukaryote
But somehow Ignicoccus evolved differently than all other archaea; somewhere along the line it developed an inner and outer membrane enclosing a huge compartment dubbed, for want of a better term, a “periplasmic space.” And, importantly, its separation of energy production and genetic material is more like that of a eukaryotic cell; which leads Dr. Huber to speculate that if eukaryotes did arise from an Archaean ancestor then an organism like I. hospitalis is an ideal candidate for such an ancestor, providing energy and other metabolites to an incorporated symbiont without requiring multiple cell membrane interactions.
Furthermore, the need for easy energy transfer from an Ignicoccus to a nanoarchaeon like N. equitans may have even driven the evolution of the larger partner’s novel architecture. Or, perhaps a dwarf Archaeon just saw an opportunity and grabbed it. “Archaea are full of surprises, as would be expected from organisms with such extreme survival talents,” according to Dr. Schaechter, who believes there are many more surprises in store.
Picture key: Ignicoccus hospitalis in cross section. The energy-making enzyme in the outer membrane, OM; the inner membrane, IM; cytoplasm, C; and intermembrane compartment, IC.
Küper U, Meyer C, Müller V, Reinhard R, Huber H: Energized outer membrane and spatial separation of metabolic processes in the hyperthermophilic Archaeon Ignicoccus in Proceedings of the National Academy of Sciences (PNAS) 2010, volume 107; pp. 3152-3156.
Junglas B, Briegel A, Burghardt T, Walther P, Wirth R, Huber H, Reinhard R: Ignicoccus hospitalis and Nanoarchaeum equitans: ultrastructure, cell-cell interaction, and 3D reconstruction from serial sections of freeze-substituted cells and by electron cytomography in Arch Microbiol 2008, volume 190; pp. 395-408.
Pace, Norman R: Problems with “Prokaryote” in Journal of Bacteriology 2009, volume 191, pp. 2008-2010.
Pace, Norman R: Time for a Change in Nature 2006, volume 441, p. 289.
Cox CJ, Foster PG, Hirt RP, Harris SR, Embley TM: The archaebacterial origin of eukaryotes in PNAS 2008, volume 105; pp. 20356-20361,
This article was originally published on Suite101.
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