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Evolution of Extremophiles

tion to extreme environments
Some microorganisms thrive under extreme
environmental conditions. Common examples
* elude the thermophiles, t e psychrophiles
and the halophiles. Most o ! ten the bacteria
with such survival capabilities are classified
among the pseudomonads, the flavobacteria
and the bacilli, although there is little apparent similarity among the individual species. It
does not seem unlikely however, that related
mechanisms may eventually be demonstrateg
to account for the diverse tolerances found to
exist in nature. Such unity of mechanism
could pr:>vide a feeble excuse for proposing
the name 5xtremophile as a descriptive for
organisms 2 Dieto populate envirohments hostile to mesophiles, or organisms which grow
only, in intermediate environments. The primary reason for suggesting this artificial classification is ease in verbal and written communication concerning them. It is obvious that
any such group cannot be considered exclusive or temporally stable.
Consideration of ths origin and evolution
of extremophiles raises the question as to
whether it is reasonable to suppose that in all
cases they evolved gradually from ancestors
which grew only in intermediate environments. Evidence seems to be accumulating
that suggests that the cellular components of
extremophiles are intrinsically stable at their
environmental extremes. This suggests either
that modern extremophiles are the result of
an accumulation of an immense number of
mutations, or that primitive organisms were
freely adaptable to a variety of environments.
In discussing the evolution of halophilism
eistad ( 1) has suggested that a relatively simple mutational eJent, resulting in a modification of the translation prol:ess, could pr educe
substitution of acidic amino acids for ba *
ones, thus accounting for the anomalous
high concentration of acidic amino acids in
the protein of extremely halophilic bacteria.
The relationship between salt tolerance and
production of acidic protein is presently obscure, but the consistancy of the observation
suggests possible significance.
No analogous consistent differences have
been detected in the protein of thermophilic
bacteria and genera1 mechanisms of thermostability remain undefined. There exist several
intriguing lines of evidence that argue for the
evolution of mesophiles from thermophilic
ancestors, rather than the converse. Thermophilic bacterial enzymes have been found to
be, with few exceptions, functional at moderate as well as at high temperature, while the
homologous mesophilic enzymes are generally
inactivated at the physiological temperatures
of the thermophiles. Interspecific relationships among the clostridial ferredoxins, as
deduced from amino acid sequence analysis,
suggests that thermophilic Clostridiaproduce
a ferredoxin which is most similar to an inferred “ primitive”
ferredoxin molecule
(Tanaka et al., 1971). The work of Brooks et
al. (1973) concerning the deduction of temperature at the time of deposition of organized fossil-like elements in the Onverwacht
group of sedimentary deposists hint at the
possible presence of bacteria-like entities in a
thermal environment over 3.35 billion years
algal phosphorylases have been
yet among the extremophiles, and the as-
Microbial adaption to extreme environments
sumption of a common mechanism of origin
is doubtful, it can be proposed that the weak
forces upon which biological
systems depend may be the key to the understanding of the functional and structural stability of macromolecules of extremophiies.
R., 1970, On the composition
%nd nature
bulk protein of extremely halophilic bacteria, Arch. hiikrobiol. 71,353-360.
Tanaka, M., M. Haniu, G. Matsueda, K.T. Yasunobu, R.H.
Himes. J.M. Akagi, E.M. Barnes and T. Devanthan, 1971,
The primary structure of the C%wtridium turtarivorwn
fe redoxin, a heat stable ferredoxin, J. biol. Chem. 24
3d 53-3960.
Brooks, J., M.D. Muir and G. Shaw, 1973, Chem::-rry and
morphology of Precambrian microorganisms. Nature 244,
Frederick, J.F., 1973, Differences of the primer-independent
isozyme in thermophilic and mesophilic
algae, Plant Cell Physioi. 14,443-448.
of the
The native enzyme is a rather large molecule which can, however, be disaggregated
into small subunits with a molecular weight
below 10,000. These subunits are obtained by
prolonged flushing of the crude enzyme preparation with buffer in an ultrafiltration
system c
ining the membranes
-10 and UM-2 coupled in !
Four fractions are obtained in this way, the
first of which contains those compounds with
a molecular weight above 50,000, the second
those between 30,000 and 50,000, the third
those between 10,000 and 30,000, and the
last one the compounds below 10,000. The
amylase activity which is at the start present
in the first fraction moves to the second and
third fraction during prolonged flushiqg, and
this fraction
exhibit enzymic
In order to determine whether the Ca functions as a co-factor or whether it had an influence on the molecular size of the enzyme
sub-unit fraction (W -2) was again plac
the vessel containing the X -50 membrane,
and passed through the same set of membranes as before for a given time. After concentrating the contents of each cell to an
volume, the activity of all four fractions
etermined in presence of Ca-ions. Another aliquot of the U -2 fraction was then
passed through the system in exactly the same
way and time, exce t that in this case Ca-ions
d to the sub-units at t
e results obtained fro
ment are the following: In the absence of Ca-
tivity declines stepwise