The
history of cyanobacteria, the photosynthetic prokaryotes, range as far as the
start of the oxygenic phase of the Earth. They were the primary generators of
oxygen when aerobic life was struggling for its rise. Cyanobacteria are the most
primitive life forms on Earth and one of the most ecologically significant
niches on Earth. They have evolved successfully and adapted themselves to each
and every changing climate. They are mostly single celled organisms but they
also exist in unicellular and filamentous forms. Their habitat includes almost
all niche of life and they populate every part of Earth. They are prokaryotic
and primary producers, which emphasizes their role as in evolving the oxygenic
environment on Earth. They photosynthesize during the day and respire in the
night and follow circadian rhythms. Cyanobacteria were the most important
organisms involved in the great Oxygenation Age. They evolved oxygen and lead
to oxygenation of the whole planet Earth. This phenomena lead to the breakdown
of methane, in the presence of molecular oxygen, into carbon dioxide and water.
The methane was impermeable to sunlight and had led to the greatest ice age of
planet Earth. When methane was broken down to water and carbon dioxide, the
carbon dioxide being not as impermeable to sunlight as methane, allowed
sunlight to pass through the upper protective layer, which in the days of
today, we call ozone and this led to the melting of glaciers and ended the
greatest ice age of history, the Huainan age. When the glaciers melted, water
came running down, multicellular organisms evolved, trees and animals started
to form. Cyanobacteria serve to advantageous organisms, not only for humans but
also for other animals. As cyanobacteria are aquatic organisms, they serve as
food for aquatic fishes and small animals. Spirulena
and Nostoc is taken as food in China
for more than two hundred years. A huge diversity of cyanobacteria exists which
serves as food for protozoa, nematodes and other soil animals. Cyanobacteria,
in addiction to chlorophyll, provide the most important group of pigment
proteins, the Phycobiliprotiens. The carotenoids serve to protect the
cyanobacteria from photo oxidative damage to nucleic acid, act in DNA repair.
The most important role of carotenoids is in light harvesting, they enhance the
light absorption spectrum of cyanobacteria. The carotenoids are actually the
hydrophobic phytochromes located in the membrane of cyanobacteria. These
carotenoids enhance the photo spectrum of cyanobacteria and allow it to absorb
light of different wave lengths. They are found in plants, animals and the
microalgae. The fact that they are so useful makes them high value commodity
products. They can also serve as colours in food additives. Many of the food
companies use synthetic colours however cyanobacteria are the natural sources
of carotenoids making them a success for commercial application. It was long
believed the cyanobacteria utilized the light between 400nm to 700nm, however,
in the recent years the new type of chlorophyll has been discovered. The new
chlorophyll is termed as chlorophyll d and chlorophyll f. The previous two
discovered complexes, chlorophyll a and chlorophyll band the phycobilisome
complexes made up the photosystem 1 and 2 and harvested light in the limited
wavelength region. i.e. 400nm to 700nm. But the recently discovered new classes
of chlorophyll have the ability to enhance the emission spectrum of chlorophyll
i.e. they absorb the infra-red light. Some researchers just believe that it’s a
modification of the previous forms of chlorophyll. Others have found it to be
the new unusual type of chlorophyll and named it chlorophyll d and f. It is the
rare type of chlorophyll that enhances the ability of bacteria to absorb
visible light. The cyanobacteria absorb light just beyond the visible spectrum
i.e. the infra-red light. The capability of the bacteria to absorb this type of
light is extremely effective for generating biofuel-algae that could absorb the
infra-red light in a greater spectrum than thought possible. The newly found
chlorophyll could absorb light in a spectrum that is detected to be about 706
Nano-meters. This is in contrast to the other types of chlorophyll, such as
chlorophyll a which absorbs the blue light in the range of 465 nanometres and
red light in 665 nanometres. Without any doubt, this new type absorbs
wavelength of red light in a spectrum that is beyond the others. The
chlorophyll d absorbs light at a wavelength of 697 nanometres, a wavelength
slightly greater than the absorbed ones with IR. The previously discovered
bacteria which had this ability didn’t have had enough of energy to split water
into H2 and O2, says Chen. Chen and his colleagues found
out the new chlorophyll from the ground up stromatolites in Western Australia
shark bay. This discovery shall also enable the scientists to generate biofuel
that was highly efficient Rachel Ehrenberg et al. Two more species
were discovered by in a 7mm thick microbial mat of Nakabusa River which was
found below the running water. This allowed the bacteria to absorb the far red
light where the visible light had less penetration. In the same mat, two
species of Leptolyngbya and two of
the Synechococcus species were
discovered. The results were in favour that the production of chlorophyll f had
enabled the bacteria to survive even in the deeper areas of soil. The results
and analysis showed that only the Leptolyngbya
strains thrived when far-red light was the only remaining source of energy.
The grown-up stromatolites were taken with a lot of chlorophyll a, and more
than often, the bacteria used either both of the two types of chlorophyll or
just one. (Satoshi Ohkubo et al. 2015).  Even though the structure and the physical and
chemical properties of the chlorophyll were solved, but the main importance of
chlorophyll f is not, till now, resolved. Various techniques employed for the
sequencing suggested that all oxygenic photo trophs were related to KC1, a Chl
f-containing cyanobacterium previously isolated from an aquatic environment.
Micro sensor measurements on  the
cyanobacterial aggregates also presented oxygenic photosynthesis at 742?nm and
less efficient photosynthesis under 768- and 777-nm light probably due to diminished
overlap with the absorption spectrum of Chl f and other far-red absorbing
pigments.  In this study, it was reported
that a unicellular Chl f-containing cyanobacterium originating from a wet
cavernous habitat and signify its ability of NIR-driven oxygenic photosynthesis.
The enrichments of the newly obtained cyanobacterium were made from a dense
dark green-blackish biofilm dominated by globular pleotypes of Nostocaceae
growing on moist limestone outside Jenolan Caves, NSW, and Australia. The
sampling site was heavily shaded even during mid-day with low irradiance levels
of 400- to 700-nm light varying from 0.5 to 5??mol photons m?2?s?1.The biofilms
of cyanobacteria were taken in the zipped bags and placed there till the
further incubation procedures. Then the samples were incubated at 28?°C in a
f/2 medium under NIR at 720?nm (?10??mol
photons m?2?s?1) yielding magnanimous green cellular aggregates after several
months of incubation. Florescent microscopy revealed the presence of orange red
florescence when excited by the blue filter. Transmission Electron Microscopy
was performed and it revealed green clusters of stacked thylakoid membranes.(Lars
Behrendt et al. February 2015). Cyanobacteria makes the use of three
major photosynthetic systems, photosystem (PS) I, PS II and phycobilisomes, to
capture and convert sunlight into chemical energy. Until recently, it was
generally thought that cyanobacteria only used light between 400?nm and 700?nm
to perform photosynthesis. However, the discovery of chlorophyll (Chl) d in Acaryochloris marina and Chl f in Halomicronema hongdechloris showed that some
cyanobacteria also consume and use as energy, the far-red light. The synthesis
of Chl f (and Chl d) is part of an extensive acclimation process, far-red light
photoacclimation (FaRLiP), which occurs in many cyanobacteria. Organisms
performing FaRLiP contain a conserved set of 17 genes encoding paralogous
subunits of the three major photosynthetic complexes. Far-red light
photoacclimation leads to the modifications in the photosystematic ability of
red light conservation. Far-red light photoacclimation seems to be regulated by
the help of a red/far-red photoreceptor, RfpA, as well as two response
regulators (Rfp B and Rfp C), one of which functions as a DNA-binding protein.
The modified photosynthetic complexes, including novel phycobiliproteins, have
the ability of absorbing light above 700?nm and allow the cells to grow in
far-red light. ). Hyperspectral microscopy (Kühl and Polerecky, 2008) of the
cyanobacterial cultures revealed distinct troughs in the transmission spectra
at absorption utmost revealing of Chl a (675–680?nm) and Chl f (?720?nm; Figure 1d, red
line). In situ spectral irradiance measurements at the sampling site showed
strong lessening of visible wavelengths in the 480- to 710-nm range whereas
highest light levels were found in the near-infrared region of the solar
spectrum at 710–900?nm. The existence of Chl a and f was further confirmed in
supplementation cultures using high-performance liquid chromatography-based
pigment analysis (Fei Gan et al. 2015). Chl b, Chl c, and Chl f are measured to
be accessory pigments found in antennae systems of the reaction centres of
photosynthetic organism. They absorb energy and transfer it to the
photosynthetic reaction centres (RC), but have no contribution in electron carriage
by the photosynthetic electron transport chain. However, Chl d as well as Chl a
can operate not only in the light gathering complex, but also in the
photosynthetic RC. The basic chemical modification of chlorophylls is the fact
that in Chl b, Chl d, and Chl f, in contrast to Chl a, a methyl or vinyl group
is replaced by a formyl group. An alteration is also possible in R4 and R5
substituents. The discovery of Chl f, a new, fifth type of chlorophyll, Chl f,
was found by a team of Australian researchers lead by Dr. Min Chen in 2010
during spectral analysis of cyanobacterial pigments of organisms capable of Chl
d synthesis. The search was directed on Western Australian coast, in the waters
of Shark Bay, where stromatolites, ancient rock like formations with a layered
structure inhabited by cyanobacteria, can be found. Morphological possessions
of stromatolites provide unique environs for the existence of various
cyanobacterial communities. The researchers cultured stromatolites samples, enlightening
them with FRL with an extreme wavelength at 720 nm which was followed by
further analysis of stromatolites methanol extract by high performance liquid
chromatography. Later, pure Chl f comprising cyanobacterial cultures Halomicronema hongdechloris were attained from Western Australia stromatolites.
In 2012, during the growing of a bottom stromatolites culture under far red
light, a Chl f consisting of filamentous cyanobacterium was taken, isolated, refined,
and categorised.  After determining
morphological characteristics and phylogenetic classification, it was selected
as H. hongdechloris. The last word, . hongdechloris , means “red
chlorophyll” in Chinese. Halomicronema
hongdechloris is the shrillest filamentous cyanobacterium known to date,
which comprises not only Chl a, but also Chl f. The pigment composition was
determined by HPLC and then absorption and luminescence spectra were examined.
Chl a, Chl f, and four types of carotenoids namely zeaxanthin, violaxanthin,
antheraxanthin, and ?carotene were found to be present. The presence of Chl f
to Chl a depends on cultivation conditions. Chl f was shown to be equal to
12.5, 20, or 10% of the total chlorophyll amount in cells cultivated under FRL enlightenment
(with extreme at 720 to730 nm), and its content is reduced to undetectable
levels in cells cultivated under white light. The ratio of carotenoids was also
reduced and the total pigment content was also decreased in cells cultivated
under white light. In this way, cells are assumed to adapt their pigment
composition to utilize ambient light in the most effective way: by accumulating
Chl f to absorb red light under the prevalence of FRL in the incident light,
and phycobiliproteins and Chl a – to absorb in the main white light range. Even
so, finest culture conditions as well as Chl f functions in H. hongdechloris are not yet studied. The contrivance
of alteration of the pigment apparatus is also unclear.

KC1 strain, in
2011, Chl f was revealed in a unicellular cyanobacterium, strain KC1, from the
fresh water Biwa Lake in Japan, Shiga Prefecture. Cells were cultured under several
radiance conditions: under white or far red light (740 nm). In both cases,
pigment investigation was led by normal phase HPLC on silica gel. In cells
grown under white light, a prevalence of Chl.a was found, whereas Chl a, and
Chl f were present as minor pigments. At the same time, Chl f? and Pheo f were
not found, as in the case of other cyanobacteria. only cells grown under FRL
illumination had Chl f as a minor pigment. The function of Chl f in these
cyanobacterial cells is still undetermined. Chl f may function not as a RC or
electron transfer chain intermediary, but as a light harvesting antenna
component. One of the key features of a cyanobacterium capable of photo
acclimation and growth under FRL is the presence of a cluster comprising of 21
genes coding photosynthetic proteins and specifically expressed under FRL. It
is to be noted that the substitution of the electron donor methyl group CH3
in ring I of Chl a by the electron acceptor formyl group CHO of Chl f causes a
shift of the Qy band to longer wavelength as well as its increase, and a short wavelength
shift of the Soret band together with its reduction . Similar effects are
observed for Chl d, whose vinyl group is exchanged by a formyl group in ring
II. Broadening of the absorption band by pigments capable of effective
photosynthesis up to 750 nm is feasible, since light intensity in the 700-750
nm region is not decreased much even at the water depth of 1 m. (S.
I. Allakhverdie et al. August 2015).