Biomedical Engineering Reference
In-Depth Information
Extremophile algae stressed by high temperatures, light, salinity, and nutrients
seem to have physiologically adapted to their harsh environmental conditions even
under high irradiation, as evidenced by a chlorophycean microalga in the storage
pools of nuclear reactors (Rivasseau et al., 2010). Because of their resilience, cultur-
ing these algae under ambient environmental conditions reduces the dependency on
seasons for cultivation and the need to shut off operations during extreme climatic
conditions. This will be cost-effective and enhance their utility in biotechnology.
The thermo-acidophilic red alga
Galderia sulphuraria
isolated from environments
with pH 0 to 4 pH and temperatures up to 56°C can survive both autotrophically
and heterotrophically (Weber et al., 2004). This alga has a repertoire of metabolic
enzymes with high potential for biotechnology. Its tolerance for high concentra-
tions of cadmium, mercury, aluminum, and nickel supports its potential for biore-
mediation. The desert crusts seem to support extremophile members of five green
algal classes; these unicellular algae growing under selective pressures of the desert
appear to have high desiccation and photophysiology tolerance (Cardon et al., 2008).
The extremophile cyanobacteria, mostly
Microcoleus
sp. living in the desert crust,
are remarkably resistant to photo-inhibition, in contrast to
Synechocystis
sp. strain
PCC 6803, and, within minutes of rehydration, recover their photosynthetic activ-
ity (Harel et al., 2004). Comparison of the extremophile
Chlamydomonas rauden-
sis
Ettl UWO 241 isolated from an ice-covered Antarctic lake with its mesophilic
counterpart
C. raudensis
Ettl. SAG 49.72 (SAG) isolated from a meadow pool in the
Czech Republic, showed different abilities for acclimation (Pocock et al., 2011). The
UWO 241 strain, unlike the other, relied on a redox sensing and signaling system for
growth that bestows better success under stressful environmental conditions.
Nannochloris
sp., isolated from the Great Salt Plains National Wildlife Refuge,
grew in salinities from 0 to 150 PSU (practical salinity unit) and temperatures up
to 45°C; growth and photosynthesis saturation were at 500 mol photons m
−2
s
−1
.
Although the division rates in this alga were equal, in cells acclimated to low or high
salinity and temperature, the former had a higher photosynthetic performance (P
max
)
than the latter (Major and Henley, 2008).
The extremophile
Coccomyxa acidophila
(pH < 2.5) accumulated more lutein
(3.55 mg g
−1
) when grown in urea (Casal et al., 2011). In another extremophile,
Chlamydomonas acidophila
(pH 2-3.5), stringent limitation of phosphate resulted
in higher total fatty acid levels and lower percentages of polyunsaturated fatty
acids (Spijkeman and Wacker, 2011).
C. acidophila
cultures grown on urea as a
carbon source yielded high biomass levels (~20 g dry biomass m
−2
d
−1
) compared to
~14 g dry biomass m
−2
d
−1
grown mixotrophically utilizing glucose as a carbon source
(Cauresma et al., 2011). Mixotrophic growth of
C. acidophila
on glucose resulted in
better accumulation of carotene and lutein (10 g kg
−1
DW), the highest recorded for
a microalga (Cauresma et al., 2011). In
Dunaliella salina
living under high light and
salt stress, carotenogenesis shifted to higher salinity and increased substantially under
nutrient-limiting conditions (Coesel et al., 2008); nutrient availability seems to control
carotenogenesis and messenger-RNA levels. The extremophile (photopsychrophile)
Chlorella
sp. Strain BI isolated from Antarctica is unique in retaining the ability for
dynamic short-term adjustment of light energy distribution between Photosystem II and
Photosystem I, and can grow as a heterotroph in the dark (Morgan-Kiss et al., 2008).
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