4
J. C. da Silva and A. T. Lombardi
1.2 Occurrence and Distribution of Chlorophylls
Algae have diverse mechanisms of photosynthesis, particularly when it comes to
light-harvesting pigments and assemblage in comparison to terrestrial plants. This
can be attributed to the different plastid types and evolutionary history, despite the
fact that endosymbiosis from Cyanobacteria and/or their ancestors are likely to have
supplied the algae with the plastids (Douglas et al. 2003).
Oxygen evolving photosynthetic organisms contains Chl a that take part in the
photochemical reactions of photosystem I (PSI), and photosystem II (PSII). Chlorophyll a is the primary photosynthetic pigment in these organisms and its concentration in microalgae is related to the mineral nutrition in culture media and exposure
light. In healthy cells, its content has been reported to constitute about 5% of the dry
biomass weight in Chlorella sp. cells (Marks 1966). Chlorophylls are located in intracellular organelles called chloroplasts, where they are attached to proteins forming
the chloroplast lamellae. These are membranes that enclose flattened “sacs” called
thylakoids (Dujardin et al. 1975), where light is absorbed during the photosynthetic
process.
The evolutionary origin of photosynthetic eukaryotes is currently explained by
the Endosymbiosis Theory, which involved capturing subsequent endosymbiosis of
prokaryotic cells, a group characterized by the absence of nucleus, Golgi complex,
endoplasmic reticulum, mitochondria, and plastids (De Duve 2007). According to
this theory, the organelles of eukaryotic cells such as mitochondria and plastids,
among them the chloroplasts, are supposed to have originated independently, from
free-living microbes (van den Hoek et al. 1995). This is supported, among other
facts, by the double-stranded DNA circular molecule similar to that of prokaryotic
cells. According to the Endosymbiosis Theory, the original plastid was derived from
Cyanobacteria ancestral that was incorporated into a eukaryotic host cell by primary
endosymbiosis; then they were gradually transformed into organelles. Once established, primary plastids spread from that lineage to other eukaryotes by additional
rounds of endosymbiosis between two eukaryotes occurred (Keeling 2004).
The primary endosymbiosis gave rise to three major clades: the green algae
(Chlorophyta), the red algae (Rhodophyta), and the Glaucocystophyta. As photoautotrophic organisms, all have Chl a; the green algae share the presence of Chl b as an
accessory pigment, while the red algae are characterized the presence of Chl c and
its derivatives as accessory photosynthetic pigments (Falkowski et al. 2004). Subsequently, secondary endosymbiotic events resulted in most algal lineages we know
today. This happened by the acquisition of plastids from the primary symbiont lineage
in association with different eukaryotic host cells (van den Hoek et al. 1995). The
secondary endosymbiotic events that involved the green algae gave rise to Euglenophytes, Chlorarachnophytes, and “green” dinoflagellates. The red primary symbiont
was engulfed in a variety of eukaryotic host cells to give rise to Cryptophytes,
Haptophytes (including coccolithophorids), Heterokonts (including diatoms), and
peridinin-containing dinoflagellates (Delwiche 1999).
J. C. da Silva and A. T. Lombardi
1.2 Occurrence and Distribution of Chlorophylls
Algae have diverse mechanisms of photosynthesis, particularly when it comes to
light-harvesting pigments and assemblage in comparison to terrestrial plants. This
can be attributed to the different plastid types and evolutionary history, despite the
fact that endosymbiosis from Cyanobacteria and/or their ancestors are likely to have
supplied the algae with the plastids (Douglas et al. 2003).
Oxygen evolving photosynthetic organisms contains Chl a that take part in the
photochemical reactions of photosystem I (PSI), and photosystem II (PSII). Chlorophyll a is the primary photosynthetic pigment in these organisms and its concentration in microalgae is related to the mineral nutrition in culture media and exposure
light. In healthy cells, its content has been reported to constitute about 5% of the dry
biomass weight in Chlorella sp. cells (Marks 1966). Chlorophylls are located in intracellular organelles called chloroplasts, where they are attached to proteins forming
the chloroplast lamellae. These are membranes that enclose flattened “sacs” called
thylakoids (Dujardin et al. 1975), where light is absorbed during the photosynthetic
process.
The evolutionary origin of photosynthetic eukaryotes is currently explained by
the Endosymbiosis Theory, which involved capturing subsequent endosymbiosis of
prokaryotic cells, a group characterized by the absence of nucleus, Golgi complex,
endoplasmic reticulum, mitochondria, and plastids (De Duve 2007). According to
this theory, the organelles of eukaryotic cells such as mitochondria and plastids,
among them the chloroplasts, are supposed to have originated independently, from
free-living microbes (van den Hoek et al. 1995). This is supported, among other
facts, by the double-stranded DNA circular molecule similar to that of prokaryotic
cells. According to the Endosymbiosis Theory, the original plastid was derived from
Cyanobacteria ancestral that was incorporated into a eukaryotic host cell by primary
endosymbiosis; then they were gradually transformed into organelles. Once established, primary plastids spread from that lineage to other eukaryotes by additional
rounds of endosymbiosis between two eukaryotes occurred (Keeling 2004).
The primary endosymbiosis gave rise to three major clades: the green algae
(Chlorophyta), the red algae (Rhodophyta), and the Glaucocystophyta. As photoautotrophic organisms, all have Chl a; the green algae share the presence of Chl b as an
accessory pigment, while the red algae are characterized the presence of Chl c and
its derivatives as accessory photosynthetic pigments (Falkowski et al. 2004). Subsequently, secondary endosymbiotic events resulted in most algal lineages we know
today. This happened by the acquisition of plastids from the primary symbiont lineage
in association with different eukaryotic host cells (van den Hoek et al. 1995). The
secondary endosymbiotic events that involved the green algae gave rise to Euglenophytes, Chlorarachnophytes, and “green” dinoflagellates. The red primary symbiont
was engulfed in a variety of eukaryotic host cells to give rise to Cryptophytes,
Haptophytes (including coccolithophorids), Heterokonts (including diatoms), and
peridinin-containing dinoflagellates (Delwiche 1999).