2. Extremophiles are organisms that can survive in
extreme environmental conditions.
Extremophiles include members of all three
domains of life, i.e., bacteria, archaea, and
eukarya.
Although the molecular strategies employed for
survival in such environments are still not fully
clarified, it is known that these organisms have
adapted biomolecules and peculiar biochemical
pathways to adapt in extreme environments.
They possess enzymes and proteins which remain
catalytically active under extremes of
temperature, salinity, pH, and solvent conditions.
3. Thermophiles are organisms that can thrive in wide
range of temperatures.
THERMOPHILES Hyperthermophile
Growth >80°C
Thermus aquaticus, Sulfolobus acidocaldarius
Thermophile
Growth 60-80°C
Bacillus subtilis, Aspergillus fumigatus
Mesophile
Growth 15-60°C
Staphylococcus aureus, Escherichia coli
Psychrophile
Growth below 15°C or lower
Pseudomonas antarctica, Psychrobacter aquaticus
5. Adaptation mechanism of Thermophiles
Membrane lipids have ether linkage- more branched,
more saturated and are of high molecular weight. These
characters increase melting temperature of membrane lipids.
Heat shock proteins- has more hydrophobic interiors which
prevents unfolding or denaturation at higher temperatures
High GC content than AT content in nucleic acid structure.
Reverse DNA gyrase enzyme- catalyzes positive
supercoiling of closed circular that helps to resist
degradation more than negatively supercoiled DNA.
6. DNA association with DNA binding histone like
protein.
Salts like potassium and magnesium are found at
higher levels in thermophilic archaea- protect double-
stranded DNA from phosphodiester bond degradation.
Thick pseudo-crystalline proteinaceous surface layer
(S-layer) surrounding cell.
Chemotrophic mode of nutrition- Can live without
sunlight or organic carbon as food- instead survive on
sulfur, hydrogen, iron sulfide and other materials that
other organisms cannot metabolize.
