Biomedical Engineering Reference
In-Depth Information
6. A two-step catalyst-free algal biodiesel production process, using wet algal
biomass and bypassing the drying and solvent extraction steps (University
of Michigan).
7. Acoustic-focusing technology that generates ultrasonic fields that concen-
trate algal cells into a dense sludge and extract oil (Solix).
Additionally, Kleinegris et al. (2011) have discussed product excretion, cell permea-
bilization, and cell death as mechanisms to extract microalgal products. They pro-
pose using two-phase systems that could circumvent the step of harvesting algal cells
while the product is extracted in situ and prepared for downstream processing.
13.8 GENETIC MODIFICATION OF ALGAE
Genome analysis is available for only four unicellular algae:
Chlamydomonas
reinhardtii,
Cyanidoschyzon merolae
,
Ostreococcus tauri,
and
Thalassiosira
pseudonana
(Misumi et al., 2008). Genetic modification (GM) of microalgae holds
promise as a strategy to attain higher lipid yields while concurrently generating
value-added products (Jin et al., 2003; León and Fernández, 2007; Gressel, 2008).
Although several hundred strains of microalgae have been cultured, detailed inves-
tigation of cellular physiology and biochemistry is limited to fewer than thirty
species. Fewer still are the algal strains that have been studied at the genomic level.
Genetic transformation of microalgae has been constrained by the presence of
rigid cell walls (Rosenberg et al., 2008). However, using a plethora of techniques
such as bombardment, electroporation, and treatment with silicon whiskers and
glass beads, several species have been modified genetically (León and Fernández,
2007), including
Amphidinium
sp
., Anabaena
sp.,
Chlamydomonas
sp.
, Chlorella
ellipsoidea, C. kessleri, C. reinhardtii
,
C. sacchrophila
,
C. sorokiniana, C. vulgaris,
Cyclotella cryptica, Cylindrotheca fusiformis, Dunaliella salina,
Euglena gracilis,
Haematococcus pluvialis, Navicula saprophila, Phaeodactylum tricornutum,
Porphyridium
sp.,
Symbiodinium microadriaticum,
Synechocystis
sp.,
Thalassiosira
weisflogii,
and
Volvox carteri.
The red alga
Cyanidoschyzon merolae
and the
euglenoid
Euglena gracilis
have also been genetically transformed (Rosenberg
et al., 2008). We agree with Pienkos et al. (2011), who suggest that through genetic
engineering a few “designer
algal strains” that have all the properties needed for
large-scale biotechnology should be developed, and more research must be carried
out in parallel with natural strains to fully understand their physiological function-
ing. Such modifications can impart properties to improve yield. For instance, Li and
Tsai i (20 08)
demonstrated that
the microalga
Nannochloropsis oculata
, which was
codon-optimized to produce bovine lactoferricin (LFB) fused with a red fluorescent
protein (DsRed), has bactericidal defense against
V. parahaemolyticus
infection in
the shrimp digestive tract.
The utility of engineered microalgae for augmented lipid biosynthesis, conver-
sion from autotrophy to heterotrophy, enhancing photosynthetic conversion effi-
ciency and expression of recombinant proteins is gaining prominence (Rosenberg
et al., 2008). While it is possible to enhance lipid synthesis through cloning acetyl-
CoA carboxylase (ACC) genes in yeast, fungi, bacteria, and a few higher plants,
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