Biomedical Engineering Reference
In-Depth Information
and nutrients. However, the molecular and genomic foundations for these inter-trait
crosstalks remain largely unknown. Second, each key microalgal trait itself is
determined or controlled by a complex set of genes or pathways. For example, at least
four known pathways interact with each other in lipid synthesis. Such complexity in
the cellular metabolic and regulatory network further confounds efforts to engineer
microalgal feedstock. Third, for oleaginous microalgae, our understanding of the
genes, pathways and genomes is quite partial and superficial. So far, there have been
relatively few genome sequences available for oleaginous microalgae. Even for the
laboratory model microalgae C. reinhardtii, a surprising large percentage of genes
(nearly 60%) are still of unknown function. Finally, the genetic engineering tool-
boxes for oleaginous microalgae have typically been preliminary or limited [
4
], at
least partially resulting from the plethora of potential oleaginous microalgal strains
and the relatively tiny size of the research community focusing on a particular strain.
Therefore, dissecting and engineering the genome-wide metabolic and regulatory
networks underpinning the complex interactions among traits and those among
genes/pathways for each trait has become an urgent mission.
3 Research Models
However, well-established research models for untangling the genome-wide
sub-cellular networks in oleaginous microalgae are still largely absent. The
prerequisite for formulating such research models is the choice of model algal strains.
First and foremost, an ideal strain for such a purpose should possess those
phenotypes that are crucial and representative in large-scale cultivation for oil
production. (1) Its potential for large-scale cultivation should have been demon-
strated in closed or open pond culture system. (2) It should harbor exceptional
phenotypes in several, if not all, of those key traits determining the technical and
economic feasibility of microalgal biofuels, such as growth rate, lipid content, bio-
mass productivity, environmental tolerance, etc. (3) It should be suitable for a wide
range of cultural and ecological conditions, such as wastewater, freshwater, brackish
(\3.5% salt), marine (3.5% salt) and hypersaline ([3.5% salt) environments. (4)
Despite the likely enormous collective metabolic capability related to lipid and
biomass production in microalgae, a model strain should harbor a certain degree of
versatility in synthesis of high-value co-products in addition to triacylglycerol, which
could reduce the overall cost of microalgal biofuel. (5) Although the metabolic and
regulatory diversity of oleaginous microalgae remains an uncharted territory, ideally
a model strain should be representative of certain metabolic and regulatory modes of
energy conversion, storage and partitioning, so that the knowledge gained on the
model strain can be readily extended to many additional strains. On the other hand, as
a research model for the dissection and engineering of genome-wide networks, it is
crucial, in terms of microalgal genotypes, that the strain features a relatively small
genome, simple gene structure, clear genetic background, abundant genomics
resources, and widely accessible methods and tools for genetic manipulation.
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