Part A | 3.5
30 Part A Marine Flora and Fauna
reported in a Flavobacterium strain [3.20]. However,
this light-dependent growth was not observed in all
proteorhodopsin-containing bacteria. A role of proteorhodopsin other than ATP synthesis was indicated,
such as the advantage for the recovery from a starvation situation [3.21]. Detailed research on the roles of
proteorhodopsin will clarify its contribution to the light
energy conversion process in marine environments.
3.4 Oxygenic Photosynthesis Using Far-Red Light (1990s–2011)
Chl a is indispensable for oxygenic photosynthesis,
since it plays an essential role in light harvesting, energy transfer, and charge separation in the primary
reaction in photosynthesis. This is based on the results from photosynthesis research using land plants
and green algae as model organisms. Quantification
of the amount of oxygenic phototrophs and the activity of oxygenic photosynthesis are, therefore, estimated
based on the amount of Chl a. The in situ light absorption range by Chl a, from 400 to 700 nm (or from
380 to 710 nm), is defined as photosynthetically active radiation (PAR). PAR is used for the evaluation
of light strength for the activity of oxygenic photosynthesis. However, a cyanobacterium Acaryochloris
marina, which performs oxygenic photosynthesis using
Chl d, was reported in 1996 [3.22]. Chl d is a redshifted chlorophyll which can absorb far-red light for
an almost 30 nm longer wavelength than Chl a [3.23].
The cyanobacterium employs Chl d not only for the
light-harvesting antenna but also for the chlorophyll
in the reaction centers [3.24, 25]. As a result, the
cyanobacterium can perform oxygenic photosynthesis
using far-red light from 700 to 740 nm, which cannot
be effectively used by common phototrophs. Acaryochloris spp. are widely distributed in coastal areas as
epiphytes on seaweed [3.26]. The amount of Chl d on
the seaweed ranges between about 113% versus total
Chl a content in seaweed. Moreover, chlorophyll was
universally detected to be about 1% (versus the Chl a
amount) in the bottom sediment of coastal areas and
lakes in the Antarctic and Arctic [3.26]. The energy
transfer efficiency of the photosynthesis using Chl d is
equivalent to that using Chl a [3.27]. Photosynthesis using far-red light, which has not been estimated at all to
date, must contribute to primary production in marine
environments.
Moreover, in 2010, another red-shifted chlorophyll,
Chl f was reported from a cyanobacterium isolated
from the microbial mat on stromatolite at the coast
of Australia [3.28]. Chl f has its absorption maximum at around 720 nm and it can absorb far-red light
up to around 760 nm in vivo. Because we have to
wait for further research to know the contribution of
Chl f to oxygenic photosynthesis in marine environments, the activity of Chl f was not taken into account
in the estimation of primary production in marine
environments.
These findings on far-red utilization using the
red-shifted chlorophylls, Chl d or Chl f , for oxygenic photosynthesis require reconsideration of the
PAR concept and primary production in marine
environments.
3.5 Discovery of Picoeukaryotic Phytoplankton (1990s–2011)
In recent years, very diverse eukaryotic picophytoplankton species have been revealed to be widely
distributed in significant amounts in marine environments. However, only some dozens of species in
chlorophyta, heterokontophyta, and haptophyta were
known as eukaryotic phytoplankton until the early
2000s.
Around 2010, several reports on marine picophytoplankton analysis using the techniques of metagenome
and flow cytometry were published. These showed
that a significant amount of picohaptophytes, including many undescribed species, were widely distributed
in marine environments. By pigment composition analysis of marine waters, a carotenoid 19
0 -hexanoyloxyfucoxanthin (19HF) was predominantly detected in the
picoplankton fraction less than 3 m at a high latitude
area from 40
ı to 60
ı of both north and south [3.29].
Since picocyanobactria, which is well known as a predominant pico-phytoplankton in tropical and subtropical marine environments, do not contain 19HF, and
19HF is a specific pigment to the algae in the Haptophyta, the amount of picophytoplankton belonging to
30 Part A Marine Flora and Fauna
reported in a Flavobacterium strain [3.20]. However,
this light-dependent growth was not observed in all
proteorhodopsin-containing bacteria. A role of proteorhodopsin other than ATP synthesis was indicated,
such as the advantage for the recovery from a starvation situation [3.21]. Detailed research on the roles of
proteorhodopsin will clarify its contribution to the light
energy conversion process in marine environments.
3.4 Oxygenic Photosynthesis Using Far-Red Light (1990s–2011)
Chl a is indispensable for oxygenic photosynthesis,
since it plays an essential role in light harvesting, energy transfer, and charge separation in the primary
reaction in photosynthesis. This is based on the results from photosynthesis research using land plants
and green algae as model organisms. Quantification
of the amount of oxygenic phototrophs and the activity of oxygenic photosynthesis are, therefore, estimated
based on the amount of Chl a. The in situ light absorption range by Chl a, from 400 to 700 nm (or from
380 to 710 nm), is defined as photosynthetically active radiation (PAR). PAR is used for the evaluation
of light strength for the activity of oxygenic photosynthesis. However, a cyanobacterium Acaryochloris
marina, which performs oxygenic photosynthesis using
Chl d, was reported in 1996 [3.22]. Chl d is a redshifted chlorophyll which can absorb far-red light for
an almost 30 nm longer wavelength than Chl a [3.23].
The cyanobacterium employs Chl d not only for the
light-harvesting antenna but also for the chlorophyll
in the reaction centers [3.24, 25]. As a result, the
cyanobacterium can perform oxygenic photosynthesis
using far-red light from 700 to 740 nm, which cannot
be effectively used by common phototrophs. Acaryochloris spp. are widely distributed in coastal areas as
epiphytes on seaweed [3.26]. The amount of Chl d on
the seaweed ranges between about 113% versus total
Chl a content in seaweed. Moreover, chlorophyll was
universally detected to be about 1% (versus the Chl a
amount) in the bottom sediment of coastal areas and
lakes in the Antarctic and Arctic [3.26]. The energy
transfer efficiency of the photosynthesis using Chl d is
equivalent to that using Chl a [3.27]. Photosynthesis using far-red light, which has not been estimated at all to
date, must contribute to primary production in marine
environments.
Moreover, in 2010, another red-shifted chlorophyll,
Chl f was reported from a cyanobacterium isolated
from the microbial mat on stromatolite at the coast
of Australia [3.28]. Chl f has its absorption maximum at around 720 nm and it can absorb far-red light
up to around 760 nm in vivo. Because we have to
wait for further research to know the contribution of
Chl f to oxygenic photosynthesis in marine environments, the activity of Chl f was not taken into account
in the estimation of primary production in marine
environments.
These findings on far-red utilization using the
red-shifted chlorophylls, Chl d or Chl f , for oxygenic photosynthesis require reconsideration of the
PAR concept and primary production in marine
environments.
3.5 Discovery of Picoeukaryotic Phytoplankton (1990s–2011)
In recent years, very diverse eukaryotic picophytoplankton species have been revealed to be widely
distributed in significant amounts in marine environments. However, only some dozens of species in
chlorophyta, heterokontophyta, and haptophyta were
known as eukaryotic phytoplankton until the early
2000s.
Around 2010, several reports on marine picophytoplankton analysis using the techniques of metagenome
and flow cytometry were published. These showed
that a significant amount of picohaptophytes, including many undescribed species, were widely distributed
in marine environments. By pigment composition analysis of marine waters, a carotenoid 19
0 -hexanoyloxyfucoxanthin (19HF) was predominantly detected in the
picoplankton fraction less than 3 m at a high latitude
area from 40
ı to 60
ı of both north and south [3.29].
Since picocyanobactria, which is well known as a predominant pico-phytoplankton in tropical and subtropical marine environments, do not contain 19HF, and
19HF is a specific pigment to the algae in the Haptophyta, the amount of picophytoplankton belonging to