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Chlorophyll (Chl) f was reported as the fifth Chl in oxygenic photoautotrophs. Chlorophyll f production expanded the utilization of photosynthetically active radiation into the far‐red light (FR) region in some cyanobacterial genera. In this study, 11 filamentous cyanobacterial strains were isolated from FR‐enriched habitats, including hydrophyte, moss, shady stone, shallow ditch, and microbial mat across Central and Southern China. Polyphasic analysis classified them into the same genus of Leptodesmis and further recognized them as four new species, including Leptodesmis atroviridis sp. nov., Leptodesmis fuscus sp. nov., Leptodesmis olivacea sp. nov., and Leptodesmis undulata sp. nov. These cyanobacteria had absorption peaks beyond 700 nm due to Chl f production and red‐shifted phycobiliprotein complexes under FR conditions. All but L. undulata produced phycoerythrin and showed varying degrees of a reddish‐brown to dark green color under white light conditions. However, the phycoerythrin contents were sharply decreased under FR conditions, and these three Leptodesmis species appeared green. In summary, the Leptodesmis genus contains diverse species with the capacity to synthesize Chl f and is likely a ubiquitous group of Chl f‐producing cyanobacteria. [ABSTRACT FROM AUTHOR]

Chlorophyll (Chl) f was recently identified in a few cyanobacteria as the fifth chlorophyll of oxygenic organisms. In this study, two Leptolyngbya‐like strains of CCNU0012 and CCNU0013 were isolated from a dry ditch in Chongqing city and a brick wall in Mount Emei Scenic Area in China, respectively. These two strains were described as new species: Elainella chongqingensis sp. nov. (Oculatellaceae, Synechococcales) and Pegethrix sichuanica sp. nov. (Oculatellaceae, Synechococcales) by the polyphasic approach based on morphological features, phylogenetic analysis of 16S rRNA gene and secondary structure comparison of 16S‐23S internal transcribed spacer domains. Both strains produced Chl a under white light (WL) but additionally induced Chl f synthesis under far‐red light (FRL). Unexpectedly, the content of Chl f in P. sichuanica was nearly half that in most Chl f‐producing cyanobacteria. Red‐shifted phycobiliproteins were also induced in both strains under FRL conditions. Subsequently, additional absorption peak beyond 700 nm in the FRL spectral region appeared in these two strains. This is the first report of Chl f production induced by FRL in the family Oculatellaceae. This study not only extended the diversity of Chl f‐producing cyanobacteria but also provided precious samples to elucidate the essential binding sites of Chl f within cyanobacterial photosystems. [ABSTRACT FROM AUTHOR]

The phenomenon of photosynthetic adaptation of cyanobacteria to far-red light (FRL; 700−750 nm) is closely related to such basic themes as: phototrophy, microbial ecology, and diversity of bacteria. In applied terms, this bioenergetic strategy is essential for biotechnology, with a perspective to possess additional photosynthetic energy. The majority of cyanobacteria is known to use 400−700 nm light, excited state being channeled from light-harvesting complex to reaction centers of two photosystems containing chlorophyll (Chl) a showing red maxima at ~700 nm. After the isolation of first strains producing Chls d and f it became clear that cyanobacteria can also use FRL. Large amount of data has been obtained on cyanobacteria which constitutively produce Chl d as well as on those strains which produce Chl f or Chl f/Chl d during FRL photoacclimation (FaRLiP). Inclusion of these pigments in photosynthetic apparatus, particularly using FaRLiP mechanisms, augments the adaptive potential of cyanobacteria and expands their distribution range. The review provides evidence on such aspects as: photosynthetic apparatus containing Chl d or Chld/Chl f; the FaRLiP gene cluster; phylogeny of cyanobacteria which constitutively or inducibly produce red-shifted chlorophylls; the use of chlorophylls in chemotaxonomy of cyanobacteria, and application of this character in nomenclature. [ABSTRACT FROM AUTHOR]

• Binding affinity differences for Chl a , d and f were calculated for PSII structures. • Chl d binds to the Chl D1 site in far-red light-absorbing PSII with high selectivity. • The calculations suggest that many sites bind a mixture of Chl a and f. [ABSTRACT FROM AUTHOR]

A few groups of cyanobacteria have been characterized as having far‐red light photoacclimation (FaRLiP) that results from chlorophyll f (Chl f) production. In this study, using a polyphasic approach, we taxonomically transferred the Cf. Leptolyngbya sp. CCNUW1 isolated from a shaded freshwater pond, which produces Chl f under far‐red light, to the genus Kovacikia and named this taxon Kovacikia minuta sp. nov. This strain was morphologically similar to Leptolyngbya‐like strains. The thin filaments were purplish‐brown under white light but became grass green under far‐red light. The 31‐gene phylogeny grouped K. minuta CCNU0001 into order Synechococcales and family Leptolyngbyaceae. Phylogenetic analysis based on 16S rRNA gene sequences further showed that K. minuta CCNU0001 was clustered into Kovacikia with similarities of 97.2–97.4% to the recently reported type species of Kovacikia muscicola HA7619‐LM3. Additionally, the internal transcribed spacer region between 16S–23S rRNA genes had a unique sequence and secondary structure compared with other Kovacikia strains and phylogenetically related taxa. Draft genome sequences of K. minuta CCNU0001 (8,564,336 bp) were assembled into one circular chromosome and two circular plasmids. A FaRLiP 20‐gene cluster comprised two operons with the unique organization. In sum, K. minuta was established as a new species, and it is the first species reported to produce Chl f and for which a draft genome was produced in genus Kovacikia. This study expanded our knowledge regarding the diversity of Chl f‐producing cyanobacteria in far‐red light‐enriched environments and provides important foundational information for future investigations of FaRLiP evolution in cyanobacteria. [ABSTRACT FROM AUTHOR]

Photosystems I and II are the photooxidoreductases central to oxygenic photosynthesis and canonically absorb visible light (400–700 nm). Recent investigations have revealed that certain cyanobacteria can acclimate to environments enriched in far-red light (700–800 nm), yet can still perform oxygenic photosynthesis in a process called far-red light photoacclimation, or FaRLiP. During this process, the photosystem subunits and pigment compositions are altered. Here, the current structural understanding of the photosystems expressed during FaRLiP is described. The design principles may be useful for guiding efforts to engineer shade tolerance in organisms that typically cannot utilize far-red light. • Some cyanobacteria acclimate to environments enriched in far-red light. • During this process, the photosystems are altered to absorb far-red light. • Cryo-EM has revealed the structures of the far-red light-absorbing photosystems. • Identifying sites that bind red-shifted chlorophylls required novel approaches. • The structures provide design principles to confer far-red light absorbance. [ABSTRACT FROM AUTHOR]

The textbook explanation that P680 pigments are the red limit to drive oxygenic photosynthesis must be reconsidered by the recent discovery that chlorophyll f (Chlf)‐containing Photosystem II (PSII) absorbing at 727 nm can drive water oxidation. Two different families of unsymmetrically substituted Zn phthalocyanines (Pc) absorbing in the 700–800 nm spectral window and containing a fused imidazole‐phenyl substituent or a fused imidazole‐hydroxyphenyl group have been synthetized and characterized as a bioinspired model of the Chlf/TyrosineZ/Histidine190 cofactors of PSII. Transient absorption studies in the presence of an electron acceptor and irradiating in the far‐red region evidenced an intramolecular electron transfer process. Visible and FT‐IR signatures indicate the formation of a hydrogen‐bonded phenoxyl radical in ZnPc II‐OH. This study sets the foundation for the utilization of a broader spectral window for multi‐electronic catalytic processes with one of the most robust and efficient dyes. [ABSTRACT FROM AUTHOR]

The textbook explanation that P680 pigments are the red limit to drive oxygenic photosynthesis must be reconsidered by the recent discovery that chlorophyll f (Chlf)‐containing Photosystem II (PSII) absorbing at 727 nm can drive water oxidation. Two different families of unsymmetrically substituted Zn phthalocyanines (Pc) absorbing in the 700–800 nm spectral window and containing a fused imidazole‐phenyl substituent or a fused imidazole‐hydroxyphenyl group have been synthetized and characterized as a bioinspired model of the Chlf/TyrosineZ/Histidine190 cofactors of PSII. Transient absorption studies in the presence of an electron acceptor and irradiating in the far‐red region evidenced an intramolecular electron transfer process. Visible and FT‐IR signatures indicate the formation of a hydrogen‐bonded phenoxyl radical in ZnPc II‐OH. This study sets the foundation for the utilization of a broader spectral window for multi‐electronic catalytic processes with one of the most robust and efficient dyes. [ABSTRACT FROM AUTHOR]

(P700+ – P700) Fourier transform visible and infrared difference spectra (DS) have been obtained using photosystem I (PSI) complexes isolated from cells of Fischerella thermalis PCC 7521 grown under white light (WL) or far-red light (FRL). PSI from cells grown under FRL (FRL-PSI) contain ~8 chlorophyll f (Chl f) molecules (Shen et al., Photosynth. Res. Jan. 2019). Both the visible and infrared DS indicate that neither the P A or P B pigments of P700 are Chl f molecules, but do support the conclusion that at least one of the A –1 cofactors is a Chl f molecule. The FTIR DS indicate that the hydrogen bond to the 131-keto C O group of the P A pigment of P700 is weakened in FRL-PSI, as might be expected given that the proteins that bind the P700 pigments are substantially different in FRL-PSI (Gan et al., Science 345, 1312–1317, 2014). The FTIR DS obtained using FRL-PSI display a band at 1664 cm−1 that is assigned (based on density functional theory calculations) to the 21-formyl C O group of Chl f , that upshifts 5 cm−1 upon P700+ formation. This is much less than expected for a cation-induced upshift, indicating that the Chl f molecule is not one of the pigments of P700. In WL-PSI the A –1 cofactor is a Chl a molecule with 131-keto and 133-methylester C O mode vibrations at 1696 and 1750 cm−1, respectively. In FRL-PSI the A –1 cofactor is a Chl f molecule with 131-keto and 133-methylester C O mode vibrations at 1702 and 1754 cm−1, respectively. Unlabelled Image • A -1 cofactor in FRL-PSI is a Chl f molecule. • The hydrogen bond to the P A pigment of P700 is weakened in FRL-PSI. • Studying FRL-PSI leads to an improved interpretation of P700 FTIR difference spectra. [ABSTRACT FROM AUTHOR]

Now is a very exciting time for those people who are interested in understanding oxygenic photosynthesis driven by longer wavelength radiation. The past two decades have seen the determination of molecular mechanisms of photosynthesis driven by long wavelengths. Apart from the characterization of additional potential of longer wavelength absorption from chlorophyll a, the two chlorophyll variants chlorophyll d and chlorophyll f were introduced with red-shifted absorption features compared to chlorophyll a and chlorophyll b, which are attributable to the position of the formyl substitutions. The maximal absorption of chlorophyll d is 697 nm, 32 nm red-shifted compared with that of chlorophyll a at 665 nm in 100% methanol; while the maximal absorption of chlorophyll f is 707 nm in methanol, red-shifted 42 nm compared with that of chlorophyll a. Chlorophyll d was reported to be widely distributed in the ecological niches with lower light intensities, but enriched by far-red wavelength light, but so far has been found only in one species of cyanobacteria, Acaryochloris marina. Chlorophyll f is co-occurring with chlorophyll a and its biosynthesis is regulated by far-red light conditions. It has been reported from various genera of cyanobacteria. [ABSTRACT FROM AUTHOR]

In cyanobacteria that undergo far red light photoacclimation (FaRLiP), chlorophyll (Chl) f is produced by the ChlF synthase enzyme, probably by photo-oxidation of Chl a. The enzyme forms homodimeric complexes and the primary amino acid sequence of ChlF shows a high degree of homology with the D1 subunit of photosystem II (PSII). However, few details of the photochemistry of ChlF are known. The results of a mutational analysis and optically detected magnetic resonance (ODMR) data from ChlF are presented. Both sets of data show that there are significant differences in the photochemistry of ChlF and PSII. Mutation of residues that would disrupt the donor side primary electron transfer pathway in PSII do not inhibit the production of Chl f , while alteration of the putative Chl Z , P680 and Q A binding sites rendered ChlF non-functional. Together with previously published transient EPR and flash photolysis data, the ODMR data show that in untreated ChlF samples, the triplet state of P680 formed by intersystem crossing is the primary species generated by light excitation. This is in contrast to PSII, in which 3P680 is only formed by charge recombination when the quinone acceptors are removed or chemically reduced. The triplet states of a carotenoid (3Car) and a small amount of 3Chl f are also observed by ODMR. The polarization pattern of 3Car is consistent with its formation by triplet energy transfer from Chl Z if the carotenoid molecule is rotated by 15° about its long axis compared to the orientation in PSII. It is proposed that the singlet oxygen formed by the interaction between molecular oxygen and 3P680 might be involved in the oxidation of Chl a to Chl f. • Mutations of key residues in Chl Z , P680 and Q A binding sites make ChlF inactive. • A triplet state similar to 3P680 is formed by ISC and not by charge recombination. • Singlet oxygen may play a role in the reaction of ChlF. • Chl Z is the most probable site of photooxidation. [ABSTRACT FROM AUTHOR]

The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Q) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria. [ABSTRACT FROM AUTHOR]

Cells of a unicellular cyanobacterium strain KC1, which were collected from Japanese fresh water Lake Biwa, formed chlorophyll (Chl) f at 6.7%, Chl a' at 2.0% and pheophytin a at 0.96% with respect to Chl a after growth under 740 nm light. The far-red-acclimated cells (Fr cells) formed extra absorption bands of Chl f at 715nm in addition to the major Chl a band. Fluorescence lifetimes were measured. The 405-nm laser flash, which excites mainly Chl a in photo-system I (PSI), induced a fast energy transfer to multiple fluorescence bands at 720-760 and 805 nm of Chl f at 77 K in Fr cells with almost no PSI-red-Chl a band. The 630-nm laser flash, which mainly excited photosystem II (PSII) through phycocyanin, revealed fast energy transfer to another set of Chl f bands at 720-770 and 810 nm as well as to the 694-nm Chl a fluorescence band. The 694-nm band did not transfer excitation energy to Chl f. Therefore, Chl a in PSI, and phycocyanin in PSII of Fr cells transferred excitation energy to different sets of Chlfmolecules. Multiple Chlf forms, thus, seem to work as the far-red antenna both in PSI and PSII. A variety of cyanobacterial species, phylogenically distant from each other, seems to use a Chl fantenna in far-red environments, such as under dense biomats, in colonies, or under far-red LED light. [ABSTRACT FROM AUTHOR]

Chlorophyll d and chlorophyll f are red-shifted chlorophylls, because their Qy absorption bands are significantly red-shifted compared with chlorophyll a. The red-shifted chlorophylls broaden the light absorption region further into far red light. The presence of red-shifted chlorophylls in photosynthetic systems has opened up new possibilities of research on photosystem energetics and challenged the unique status of chlorophyll a in oxygenic photosynthesis. In this review, we report on the chemistry and function of red-shifted chlorophylls in photosynthesis and summarise the unique adaptations that have allowed the proliferation of chlorophyll d- and chlorophyll f-containing organisms in diverse ecological niches around the world. [ABSTRACT FROM AUTHOR]

Cyanobacteria have evolved a number of acclimation strategies to sense and respond to changing nutrient and light conditions. Leptolyngbya sp. JSC-1 was recently shown to photoacclimate to far-red light by extensively remodeling its photosystem (PS) I, PS II and phycobilisome complexes, thereby gaining the ability to grow in far-red light. A 21-gene photosynthetic gene cluster (rfpA/B/C, apcA2/B2/D2/E2/D3, psbA3/D3/C2/B2/ H2/A4, psaA2/B2/L2/I2/F2/J2) that is specifically expressed in far-red light encodes the core subunits of the three major photosynthetic complexes. The growth responses to far-red light were studied here for five additional cyanobacterial strains, each of which has a gene cluster similar to that in Leptolyngbya sp. JSC-1. After acclimation all five strains could grow continuously in far-red light. Under these growth conditions each strain synthesizes chlorophylls d, f and a after photoacclimation, and each strain produces modified forms of PS I, PS II (and phycobiliproteins) that absorb light between 700 and 800 nm. We conclude that these photosynthetic gene clusters are diagnostic of the capacity to photoacclimate to and grow in far-red light. Given the diversity of terrestrial environments from which these cyanobacteria were isolated, it is likely that FaRLiP plays an important role in optimizing photosynthesis in terrestrial environments. [ABSTRACT FROM AUTHOR]

We report production of chlorophyll f and chlorophyll d in the cyanobacterium Chlorogloeopsis fritschii cultured under near-infrared and natural light conditions. C. fritschii produced chlorophyll f and chlorophyll d when cultured under natural light to a high culture density in a 20 L bubble column photobioreactor. In the laboratory, the ratio of chlorophyll f to chlorophyll a changed from 1:15 under near-infrared, to an undetectable level of chlorophyll f under artificial white light. The results provide support that chlorophylls f and d are both red-light inducible chlorophylls in C. fritschii . [ABSTRACT FROM AUTHOR]

Abstract: A Chl f-containing filamentous cyanobacterium was purified from stromatolites and named as Halomicronema hongdechloris gen., sp. nov. after its phylogenetic classification and the morphological characteristics. Hongdechloris contains four main carotenoids and two chlorophylls, a and f. The ratio of Chl f to Chl a is reversibly changed from 1:8 under red light to an undetectable level of Chl f under white-light culture conditions. Phycobiliproteins were induced under white light growth conditions. A fluorescence emission peak of 748nm was identified as due to Chl f. The results suggest that Chl f is a red-light inducible chlorophyll. [Copyright &y& Elsevier]

Abstract: Both chlorophyll f and chlorophyll d are red-shifted chlorophylls in oxygenic photosynthetic organisms, which extend photon absorbance into the near infrared region. This expands the range of light that can be used to drive photosynthesis. Quantitative determination of chlorophylls is a crucial step in the investigation of chlorophyll-photosynthetic reactions in the field of photobiology and photochemistry. No methods have yet been worked out for the quantitative determination of chlorophyll f. There is also no method available for the precise quantitative determination of chlorophyll d although it was discovered in 1943. In order to obtain the extinction coefficients (ε) of chlorophyll f and chlorophyll d, the concentrations of chlorophylls were determined by Inductive Coupled Plasma Mass Spectrometry according to the fact that each chlorophyll molecule contains one magnesium (Mg) atom. Molar extinction coefficient εchl f is 71.11×103 Lmol−1 A707nm cm−1 and εchl d is 63.68×103 Lmol−1 A697nm cm−1 in 100% methanol. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. [Copyright &y& Elsevier]

[Display omitted] • High-precision modeling of Q y band of chlorophylls a , d and f was performed. • Vertical excitation energies difference is the main reason in the band shifts. • Vibronic structures of Q y band of chlorophylls a , d and f are similar. The key components of the far-red-light forms of PSI and PSII are chlorophylls d and f which are able to absorb this light contrary to chlorophyll a. The aim of this work is to reveal the origin of their absorbance shift. XMCQDTP2/SA-CASSCF with large number of active valence orbitals results were found to be in a good agreement with the experimental data. The modeling of the main peak of Q y band has shown that absorbance shift is mainly due to the difference of vertical excitation energies, while the vibronic structure of this peak is quite similar for all three molecules. [ABSTRACT FROM AUTHOR]

Inside Back Cover: Phthalocyanine as a Bioinspired Model for Chlorophyll f-Containing Photosystem II Drives Photosynthesis into the Far-Red Region (Angew. Bioinspired models, chlorophyll f, far-red region, photosystem II, phthalocyanine Keywords: bioinspired models; chlorophyll f; far-red region; photosystem II; phthalocyanine EN bioinspired models chlorophyll f far-red region photosystem II phthalocyanine 12607 12607 1 05/20/21 20210525 NES 210525 B Chlorophyll b f (Chl I f i )-containing Photosystem II absorbing in the far red has transgressed the red limit of photosynthesis locked by chlorophyll I a i at 680 nm and drives water oxidation at 727 nm. [Extracted from the article]

Keywords: bioinspired models; chlorophyll f; far-red region; photosystem II; phthalocyanine EN bioinspired models chlorophyll f far-red region photosystem II phthalocyanine 12715 12715 1 05/20/21 20210525 NES 210525 B Das Chlorophyll f b (Chl I f i ) enthaltende Photosystem II, das im fernen Rot absorbiert, überwindet das "rote Limit" der Photosynthese, das vom Chlorophyll I a i bei 680 nm festgelegt ist, und vermittelt die Wasseroxidation bei 727 nm. Innenrücktitelbild: Phthalocyanine as a Bioinspired Model for Chlorophyll f-Containing Photosystem II Drives Photosynthesis into the Far-Red Region (Angew. Bioinspired models, chlorophyll f, far-red region, photosystem II, phthalocyanine. [Extracted from the article]

The Photosystem I (PSI) reaction center in cyanobacteria is comprised of ~96 chlorophyll (Chl) molecules, including six specialized Chl molecules denoted Chl 1A/ Chl 1B (P 700), Chl 2A/ Chl 2B, and Chl 3A/ Chl 3B that are arranged in two branches and function in primary charge separation. It has recently been proposed that PSI from Chroococcidiopsis thermalis (Nürnberg et al. (2018) Science 360, 1210–1213) and Fischerella thermalis PCC 7521 (Hastings et al. (2019) Biochim. Biophys. Acta 1860, 452–460) contain Chl f in the positions Chl 2A/ Chl 2B. We tested this proposal by exciting RCs from white-light grown (WL-PSI) and far-red light grown (FRL-PSI) F. thermalis PCC 7521 with femtosecond pulses and analyzing the optical dynamics. If Chl f were in the position Chl 2A/ Chl 2B in FRL-PSI, excitation at 740 nm should have produced the charge-separated state P 700 +A 0 − followed by electron transfer to A 1 with a τ of ≤25 ps. Instead, it takes ~230 ps for the charge-separated state to develop because the excitation migrates uphill from Chl f in the antenna to the trapping center. Further, we observe a strong electrochromic shift at 685 nm in the final P 700 +A 1 − spectrum that can only be explained if Chl a is in the positions Chl 2A/ Chl 2B. Similar arguments rule out the presence of Chl f in the positions Chl 3A/ Chl 3B; hence, Chl f is likely to function solely as an antenna pigment in FRL-PSI. We additionally report the presence of an excitonically coupled homo- or heterodimer of Chl f absorbing around 790 nm that is kinetically independent of the Chl f population that absorbs around 740 nm. • Function of Chl f in Photosystem I from Fischerella thermalis PCC 7521 was studied. • Femtosecond optical dynamics rule out the function of Chl f in electron transfer. • Uphill excitation transfer from Chl f and charge separation in RC proceeds at 230 ps. • The primary ion-radical state P 700 +A 0 − is in fast equilibrium with excited antenna. [ABSTRACT FROM AUTHOR]

We present ground and excited state frequency calculations of the recently discovered extremely red-shifted chlorophyll f. We discuss the experimentally available vibrational mode assignments of chlorophyll f and chlorophyll a which are characterised by particularly large downshifts of 131-keto mode in the excited state. The accuracy of excited state frequencies and their displacements are evaluated by the construction of Franck–Condon (FC) and Herzberg–Teller (HT) progressions at the CAM-B3LYP/6-31G(d) level. Results show that while CAM-B3LYP results are improved relative to B3LYP calculations, the displacements and downshifts of high-frequency modes are underestimated still, and that the progressions calculated for low temperature are dominated by low-frequency modes rather than fingerprint modes that are Resonant Raman active. [ABSTRACT FROM AUTHOR]

We examined energy transfer dynamics in the unique chlorophyll (Chl) f-containing cyanobacterium Halomicronema hongdechloris. The absorption band of Chl f appeared during cultivation of this organism under far-red light. The absorption maximum of Chl f in organic solvents occurs at a wavelength of approximately 40 nm longer than that of Chl a. In vivo, the cells display a new absorption band at approximately 730 nm at 298 K, which is at a significantly longer wavelength than that of Chl a. We primarily assigned this band to a long wavelength form of Chl a. The function of Chl f is currently unknown. We measured the fluorescence of cells using time-resolved fluorescence spectroscopy in the picosecond-to-nanosecond time range and found clear differences in fluorescence properties between the cells that contained Chl f and the cells that did not. After excitation, the fluorescence peaks of photosystem I and photosystem II appeared quickly but diminished immediately. A unique fluorescence peak located at 748 nm subsequently appeared in cells containing Chl f. This finding strongly suggests that the Chl f in this alga exists in photosystem I and II complexes and is located close to each molecule of Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. [ABSTRACT FROM AUTHOR]