Marine Micro
51
Part A | 5.2
5. Marine Microalgae
Tsuyoshi Tanaka, Masaki Muto, Yue Liang, Tomoko Yoshino, Tadashi Matsunaga
Marine microalgae, the largest primary producer
in the marine system, have been attracting wide
attention as potential resources of new metabolites and biofuels. Whole genome sequencing and
genetic modifications of microalgae have been
rapidly advancing during the last few decades.
In this chapter, the diversity of marine microalgae, the microalgal natural components, and the
biotechnologies associated with microalgae are
reviewed.
5.1 Overview ................................................ 51
5.2 Marine Microalgae .................................. 52
5.3 Microalgal Genomes ................................ 53
5.4 Genetic Engineering of Microalgae........... 54
5.4.1 Genetic Transformation Methods ..... 54
5.4.2 Metabolic Engineering.................... 56
5.5 Photobioreactors for Marine Microalgae ... 57
References..................................................... 58
5.1 Overview
Algae are the primary producers of oxygen in the
aquatic environment. These microorganisms are widely
distributed in marine systems and have a great diversity
with respect to size, morphology, life cycle, pigments,
and metabolism. About half of the global oxygen production is accomplished by marine microalgae. They
play an important role in CO 2 recycling through photosynthesis, which is similar to higher plants in O 2 -
evolved systems (PSI (photosystem I) and PSII (photosystem II)). In addition to having a long history of use
as food and as live feed in aquaculture, microalgae have
also been considered as a promising source for highvalue added products for pharmaceuticals, cosmetics,
and other industrial applications, such as ˇ-carotene,
astaxanthin, polyunsaturated fatty acids (PUFAs). The
utilization of microalgae as a suitable feedstock for
sustainable biofuel production has gained worldwide
attention over the last 20 years. In general, microalgal triacylglycerols, hydrocarbons, and polysaccharides
are considered as biofuel precursors. Alkanes and short
chain fatty acid methyl esters (FAMEs), ranging from
C9 to C17, have been considered as the potential alternative jet fuel, while those ranging from C9 to C23
have been mainly recognized as biodiesel. FAMEs are
normally generated from the methyl esterification of
triacylglycerols. On the other hand, with the degradation and fermentation of microalgal polysaccharides,
the generated ethanol can be used as an alternative
fuel to gasoline. Compared with higher plants, biofuel from microalgae has two advantages: 1) a relatively higher productivity, and 2) no competition to
agriculture.
On the other hand, increased reports of the microalgal whole genome sequence data have been significantly facilitating the better understanding of their
evolutionary lineage and the species specificity of the
microalgal metabolic pathway. In addition, gene transformation has been achieved in 18 microalgal genera.
In this chapter, we reviewed the fundamental characteristics of marine microalgae, the useful microalgal
natural products, as well as the biotechnological aspects
of marine microalgae.
51
Part A | 5.2
5. Marine Microalgae
Tsuyoshi Tanaka, Masaki Muto, Yue Liang, Tomoko Yoshino, Tadashi Matsunaga
Marine microalgae, the largest primary producer
in the marine system, have been attracting wide
attention as potential resources of new metabolites and biofuels. Whole genome sequencing and
genetic modifications of microalgae have been
rapidly advancing during the last few decades.
In this chapter, the diversity of marine microalgae, the microalgal natural components, and the
biotechnologies associated with microalgae are
reviewed.
5.1 Overview ................................................ 51
5.2 Marine Microalgae .................................. 52
5.3 Microalgal Genomes ................................ 53
5.4 Genetic Engineering of Microalgae........... 54
5.4.1 Genetic Transformation Methods ..... 54
5.4.2 Metabolic Engineering.................... 56
5.5 Photobioreactors for Marine Microalgae ... 57
References..................................................... 58
5.1 Overview
Algae are the primary producers of oxygen in the
aquatic environment. These microorganisms are widely
distributed in marine systems and have a great diversity
with respect to size, morphology, life cycle, pigments,
and metabolism. About half of the global oxygen production is accomplished by marine microalgae. They
play an important role in CO 2 recycling through photosynthesis, which is similar to higher plants in O 2 -
evolved systems (PSI (photosystem I) and PSII (photosystem II)). In addition to having a long history of use
as food and as live feed in aquaculture, microalgae have
also been considered as a promising source for highvalue added products for pharmaceuticals, cosmetics,
and other industrial applications, such as ˇ-carotene,
astaxanthin, polyunsaturated fatty acids (PUFAs). The
utilization of microalgae as a suitable feedstock for
sustainable biofuel production has gained worldwide
attention over the last 20 years. In general, microalgal triacylglycerols, hydrocarbons, and polysaccharides
are considered as biofuel precursors. Alkanes and short
chain fatty acid methyl esters (FAMEs), ranging from
C9 to C17, have been considered as the potential alternative jet fuel, while those ranging from C9 to C23
have been mainly recognized as biodiesel. FAMEs are
normally generated from the methyl esterification of
triacylglycerols. On the other hand, with the degradation and fermentation of microalgal polysaccharides,
the generated ethanol can be used as an alternative
fuel to gasoline. Compared with higher plants, biofuel from microalgae has two advantages: 1) a relatively higher productivity, and 2) no competition to
agriculture.
On the other hand, increased reports of the microalgal whole genome sequence data have been significantly facilitating the better understanding of their
evolutionary lineage and the species specificity of the
microalgal metabolic pathway. In addition, gene transformation has been achieved in 18 microalgal genera.
In this chapter, we reviewed the fundamental characteristics of marine microalgae, the useful microalgal
natural products, as well as the biotechnological aspects
of marine microalgae.