Environmental Engineering Reference
In-Depth Information
partially be secondary effects of protein stabilization (e.g., stabilization of mem-
brane proteins) in microorganisms. Extremolytes provide protection to this cells
against drying environment probably by replacing of water molecules by hydroxyl
group of Ectoine [59] and thus stabilize membrane fluidity. Hydroxyectoine (4S-2-
methyl-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid) was originally discovered
from an extremely halophilic phototrophic eubacterium
Halorhodospira halochlo-
ris
, isolated from Wadi Natrun, Egypt by Galinski et al. [33]. Later, hydroxyectoine
substance was also found in a wide varieties of halophilic and halotolerant bacte-
ria. The ability to accumulate ectoine was observed among the organisms such as
E. coli
,
B. subtilis
,
C. glutamicum
, and
S. melilotii
[46, 86].
The carbohydrate extremolytes such as mannosylglycerate (Firoin) and manno-
sylglyceramide (Firoin-A) are among top value-added extremolytes. Firoin accumu-
lates in the cells in response to heat stress in thermophilic microbes. The chemically
reactive end of the sugar of firoin forms a glycosidic bond with a hydroxyl group
of glyceric acid or glyceramide.
Rhodothermus marinus
synthesizes both manno-
sylglycerate and mannosylglyceramide. Anionic mannosylglycerate is accumulated
in the cells in response to heat stress. Whereas, uncharged mannosylglyceramide
increase in the cells with elevated NaCl levels. Mannosylglycerate was also found
in eukaryotic mesosphilic red algae [49].
Archaeabacteria are well known as extremophilic candidates among the microor-
ganisms. Typical halotolerant and hyperthermophilic archeabacteria
Pyrococcus
furiosus
and
Thermotoga maritima
accumulate negatively charged derivatives
of inositol and glycerol at extreme temperature and high salt concentration
[22, 82]. Di-myoinositol-1,1
-phosphate (DIP), a phosphodiester derivative of
the uncharged osmolyte myoinositol found in eukaryotes, which provides tol-
erance against salinity.
-Diglycerol phosphate (DGP) was identified as a new
extremolyte in
Archaeoglobus fulgidus
and shown to be an effective protein sta-
bilizer in vitro [56, 73]. DGP is also known to accumulate in response to elevated
external NaCl concentrations, while temperature increases lead to enhanced DIP
accumulation [55]. Similarly, cyclic 2,3-diphosphoglycerate (cDPG) and cyclic tri-
anionic pyrophosphate were found to accumulate in archaea
Methanothermobacter
thermoautotrophicus
. The primary role of 2,3-diphosphoglycerate (cDPG), in
Methanothermobacter
may be as a phosphate storage compound which may pro-
vide protection to glyceraldehyde-3-phosphate dehydrogenases at high temperature
[42, 66]. Other novel extremolytes and their applications are being summarized in
theTable2.
Besides conventional means, non conventional sources such as marine macro
and micro flora have been explored to isolate the novel drug candidates to inhibit
or activate the vital signalling pathways lead to cure or prevent the particular dis-
eases or disorder. Bryostatins, isolated from bryozoan,
Bugula neritina,
one of the
novel protein kinase C (PKC) inhibitors is being evaluated for cancer cure. The
marine microalgae, cyanobacteria, and heterotrophic bacteria, living in association
with invertebrates (e.g. sponges, tunicates, and soft corals etc.) have been identi-
fied, as the original sources of many bioactive compounds
(
Kahalalide F, E7389,
Curacin A, Salinosporamide A and Eleutherobin
)
and may be used as important
γ
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