Environmental Engineering Reference
In-Depth Information
for “extremophile” status of any organism. UV and ionizing radiation have impor-
tance in medicine, energy production, warfare and space programmes. However, the
ionizing radiation causes oxidative damage among the vital biomolecules including
proteins and nucleic acid. However, it is not unclear how the bacterium
D. radio-
durans
can grow against supra-lethal ionizing radiation (up to 20 kGy of gamma
radiation) and UV radiation (doses up to 1,000 J m) [9]. The extraordinary resistance
of
D. radiodurans
is thought to be a by-product of its resistance against extreme
desiccation. Other organisms that can stand high levels of radiation are
Rubrobacter
species [32] and the green alga
Dunaliella bardawil
[10].
In space research, planet 'Mars' atmosphere has a very thin ozone layer that
changes with seasons and thus may be unable to protect potential mars micro biota
if they exist [23, 57]. Endolithic cyanobacteria have been suggested as the ideal
models for Martian biota by astrobiologists. These cynobacteria have the ability
to protect themselves from UV rays by the producing photo-protective pigments.
Desiccation- resistant strains of the cyanobacterium
Chroococcidiopsis
also exhibit
resistance against ionizing radiation probably due to efficient DNA repair mecha-
nisms [14]. Biosynthesis of radiation responsive pigments and DNA repair enzymes
could be induced or activated by modern biotechnological techniques.
2.1.3 Desiccation
Water is an essential component of life under natural environment, however it gen-
erates extreme environments due to its insufficiency. Organisms that are able to
tolerate extreme desiccation develop anhydrobiosis, a state characterized by little
intracellular water with metabolically inactive life. Numerous organisms includ-
ing bacteria, yeast, and fungi, are able to adopt anhydrobiotics, sustainable life
[79]. In un-adapted situation, anhydrobiosis induced irreversible changes in the cell
membrane's lipids, proteins and nucleic acids lead to denaturation and structural
breakage through Maillard reactions leading to the cell death. Anhydrobiosis also
induce accumulation of reactive oxygen species during drying; especially the solar
radiation is among major reasons of death in desiccated environment [28].
2.1.4 Pressure
Terrestrial life originated at an atmospheric pressure equal to 101 kPa (1 atmo-
sphere
1.013 bar). Hydrostatic pressures are estimated to be increase at a rate
of 10.5 kPa per metre depth, as compared with lithostatic pressure which increased
at the rate of 22.6 kPa per metre. The pressure decreases with the increased alti-
tude so that at 10 km above sea level, the atmospheric pressure is almost a one
third of sea level. The change in pressure challenges life at the cellular level by
compressing the packing of cell membrane lipids resulting in decreased membrane
fluidity [7]. Many organisms have ability to survive at high pressure such as obliga-
tory piezophilic species can grow at 70 to 80 MPa, though unable to sustain below
50 MPa [50]. Gravity is an integral component of the pressure. Organisms including
human beings live on earth at 1
g
. The effect of gravity and atmospheric pressure on
=
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