Biomedical Engineering Reference
In-Depth Information
Thermophiles
Of all the extremophiles, thermophiles are amongst the best studied, thriving in
temperatures above 45 C, with some of their number, termed hyperthermophiles,
prefer temperatures in excess of 85 C. Unsurprisingly, the majority of them
have been isolated from environments which have some association with vol-
canic activity. The first extremophile capable of growth at temperatures greater
than 70 C was identified in the late 1960s as a result of a long-term study of
life in the hot-springs of Yellowstone National Park, Wyoming USA, headed by
Thomas Brock of the University of Wisconsin-Madison. Now known as Thermus
aquaticus , this bacterium would later make possible the widespread use of a rev-
olutionary technology, the polymerase chain reaction (PCR), which is returned
to later in this chapter. Shortly after this initial discovery, the first true hyper-
thermophile was found, this time an archaean which was subsequently named
Sulfolobus acidocaldarius . Having been discovered in a hot acidic spring, this
microbe thrives in temperatures up to 85 C. Hyperthermophiles have since been
discovered from deep sea vent systems and related features such as geothermal
fluids, attached sulphide structures and hot sediments. Around 50 species are
presently known. Some grow and reproduce in conditions hotter than 100 C, the
current record being held by Pyrolobus fumarii , which was found growing in
oceanic 'smokers'. Its optimum temperature for reproduction is around 105 C
but will continue to multiply up to 113 C. It has been suggested that this rep-
resents merely the maximum currently accepted for an isolated and culturable
hyperthermophile and is probably not even close to the upper temperature limit
for life which has been postulated at around 150 C, based on current understand-
ing. Although no one knows for certain at this time, it is widely thought that
higher than this the chemical integrity of essential molecules will be unlikely to
escape being compromised.
To set this in context, isolated samples of common place proteins, like egg albu-
min, are irreversibly denatured well below 100 C. The more familiar mesophilic
bacteria enjoy optimum growth between 25 and 40 C; no known multicellular
organism can tolerate temperatures in excess of 50 C and no eukaryotic microbe
known can survive long term exposure to temperatures greater than around 60 C.
The potential for the industrial exploitation of the biochemical survival mech-
anisms which enable thermo- and hyperthermophiles to thrive under such hot
conditions is clear. In this respect, the inactivation of thermophiles at temper-
atures which are still too hot for other organisms to tolerate may also have
advantages in commercial processes. Though an extreme example in a world of
extremes, the previously mentioned P. fumarii , stops growing below 90 C; for
many other species the cut-off comes at around 60 C.
A good understanding of the way in which extremophile molecules are able to
function under these conditions is essential for any future attempt at harnessing
the extremozymes for industrial purposes. One area of interest, in particular is
how the structure of molecules in these organisms, which often very closely
resemble their counterparts in mesophilic microbes, influences activity. In a
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