4. Improvement in high and/or low temperature tolerance in
oil-rich microalgae by genetic and metabolic engineering
methods
5. Development of low-cost technologies for biomass harvesting,
drying, and oil extraction.
Among the abovementioned strategies, metabolic engineering
combined with genetic engineering could be regarded very
promising as the host metabolism system could be manipulated
extensively to achieve several attributes of interest simultaneously.
Examples of such attributes include improved production yield,
decreased production of unfavorable by-products, ability to use a
wide spectrum of carbon sources, and resistance to environmental
conditions (such as high/low temperatures, wide pH range, and
toxic substances) [14].
Optimizing flux and/or overexpression/deletion of genes
encoding specific enzymes or regulating their expression rates are
the main methods to manipulate biochemical pathways of microalgae through metabolic engineering. It should be highlighted that
it has also become technically feasible to introduce the entire metabolic pathways of a microorganism in a superior host organism
through synthetic biology [6, 15, 16]. Overall, such efforts are
aimed at reconstructing or reengineering metabolic pathways in
order to achieve algal cells possessing favorable features [17]. In
order to ensure that an effective biochemical pathway would be
constructed and desired products would be generated, selection of
an appropriate algal host and targeting an appropriate pathway are
critical. Besides that, it is important to achieve a stable montage of
heterologous DNA fragment into the algal host. The complex
nature of metabolic pathways (obviously owing to the involvement
of many genes and enzymes) and occasionally occurring unfavorable feedback responses such as inhibition feedback have rendered
construction/re-construction of pathways capable of effective biofuel production, an uphill task [6, 18, 19].
2 Metabolic Engineering for Biodiesel Production by Microalgae
Like canola and sunflower, microalgae can also produce triglycerides. The oil content of microalgae can be as high as 30–70% of
their dry biomass under suitable conditions, and this has been the
source of interest for biodiesel production [16, 20, 21]. Lipid
metabolism pathway is very important in fuel extraction from
microalgae and can be considered as a highly complex and tightly
regulated pathway. This pathway is also diverse among various
microalgae species due to the metabolic divergence between the
phylogenetic groups [1, 17]. Moreover, an elaborated regulatory
network of nodes and internodes adds to the already difficult task of
Metabolic Engineering of Microalgae
155
oil-rich microalgae by genetic and metabolic engineering
methods
5. Development of low-cost technologies for biomass harvesting,
drying, and oil extraction.
Among the abovementioned strategies, metabolic engineering
combined with genetic engineering could be regarded very
promising as the host metabolism system could be manipulated
extensively to achieve several attributes of interest simultaneously.
Examples of such attributes include improved production yield,
decreased production of unfavorable by-products, ability to use a
wide spectrum of carbon sources, and resistance to environmental
conditions (such as high/low temperatures, wide pH range, and
toxic substances) [14].
Optimizing flux and/or overexpression/deletion of genes
encoding specific enzymes or regulating their expression rates are
the main methods to manipulate biochemical pathways of microalgae through metabolic engineering. It should be highlighted that
it has also become technically feasible to introduce the entire metabolic pathways of a microorganism in a superior host organism
through synthetic biology [6, 15, 16]. Overall, such efforts are
aimed at reconstructing or reengineering metabolic pathways in
order to achieve algal cells possessing favorable features [17]. In
order to ensure that an effective biochemical pathway would be
constructed and desired products would be generated, selection of
an appropriate algal host and targeting an appropriate pathway are
critical. Besides that, it is important to achieve a stable montage of
heterologous DNA fragment into the algal host. The complex
nature of metabolic pathways (obviously owing to the involvement
of many genes and enzymes) and occasionally occurring unfavorable feedback responses such as inhibition feedback have rendered
construction/re-construction of pathways capable of effective biofuel production, an uphill task [6, 18, 19].
2 Metabolic Engineering for Biodiesel Production by Microalgae
Like canola and sunflower, microalgae can also produce triglycerides. The oil content of microalgae can be as high as 30–70% of
their dry biomass under suitable conditions, and this has been the
source of interest for biodiesel production [16, 20, 21]. Lipid
metabolism pathway is very important in fuel extraction from
microalgae and can be considered as a highly complex and tightly
regulated pathway. This pathway is also diverse among various
microalgae species due to the metabolic divergence between the
phylogenetic groups [1, 17]. Moreover, an elaborated regulatory
network of nodes and internodes adds to the already difficult task of
Metabolic Engineering of Microalgae
155