Fundamentals of Biological Intervention - Environmental Biotechnology: Theory and Application - page 53

their counterparts in mesophilic microbes, influences activity. In a number of
heat-tolerant extremozymes, for example, the major difference appears to be no
more than an increased prevalence of ionic bonds within the molecule.
Though the industrial use of extremophiles in general has been limited to date,
it has notably given rise to polymerase chain reaction (PCR), a major technique
used in virtually every molecular biology laboratory worldwide. The application
of PCR has, in addition, opened the flood gates for the application of genetic
analyses in many other branches of life science, including forensics and medical
diagnosis. Though this is a tool of genetic engineering rather than anything which
could be argued as an 'environmental' application, it does illustrate the enormous
potential of extremozymes. The process uses a DNA polymerase, called Taq poly-
merase, derived from T. aquaticus , as mentioned earlier, and was invented by
Kary Mullins in the mid-1980s. The original approach relied on mesophilic poly-
merases and since the reaction mixture is alternately cycled between low and high
temperatures, enzymatic denaturation took place, requiring their replenishment at
the end of each hot phase. Samples of T. aquaticus had been deposited shortly
after the organism's discovery, some 20 years earlier, and the isolation of its
highly heat-tolerant polymerase enabled totally automated PCR technology to be
developed. In recent years, some PCR users have begun to substitute Pfu poly-
merase, isolated from another hyperthermophile, Pyrococcus furiosus , which has
an optimum temperature of 100 ◦ C.
Other extremophiles
As was stated earlier, the thermophiles are amongst the best investigated of the
extremophiles, but there are many other species which survive under equally
challenging environmental conditions and which may also have some potential
as the starting point for future methods of reduced pollution manufacturing. For
example, cold environments are more common on earth than hot ones. The aver-
age oceanic temperature is around 1-3 ◦ C and vast areas of the global land mass
are permanently or near-permanently frozen. In these seemingly inhospitable con-
ditions, extremophiles, known as psychrophiles, flourish. A variety of organisms
including a number of bacteria and photosynthetic eukaryotes can tolerate these
circumstances, often with an optimum functional temperature as low as 4 ◦ Cand
stopping reproduction above 12 or 15 ◦ C. Intensely saline environments, such
as exist in natural salt lakes or within the artificial confines of constructed salt
evaporation ponds are home to a group of extremophiles, termed the halophiles.
Under normal circumstances, water flows from areas of low solute concentra-
tion to areas where it is higher. Accordingly, in salty conditions, unprotected
cells rapidly lose water from their cytoplasm and dehydrate. Halophilic microbes
appear to deal with this problem by ensuring that their cytoplasm contains a
higher solute concentration than is present in their surroundings. They seem to
achieve this by two distinct mechanisms, either manufacturing large quantities of
solutes for themselves or concentrating a solute extracted from external sources.