52 Environmental Biotechnology
Thermophiles
Of all the extremophiles, thermophiles are amongst the best studied, thriving
in temperatures above 45◦C, while some of their number, termed hyperther-
mophiles, prefer temperatures in excess of 85◦C. Unsurprisingly, the majority
of them have been isolated from environments which have some association
with volcanic 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
asThermus aquaticus, this bacterium would later make possible the widespread
use of a revolutionary technology, the polymerase chain reaction (PCR), which
is returned to later in this chapter. Shortly after this initial discovery, the first
true hyperthermophile was found, this time an archaean which was subsequently
namedSulfolobus 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 geother-
mal 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 byPyrolobus 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 commonplace proteins, like egg albu-
min, are irreversibly denatured well below 100◦C. The more familiar mesophilic
bacteria enjoy optimum growth between 25–40◦C; no known multicellular organ-
ism 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 mentionedP. 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