. After determining morphologicalcharacteristics and phylogenetic classification, it was selected as H.
hongdechloris. The last word, . hongdechloris , means “redchlorophyll” in Chinese. Halomicronemahongdechloris is the shrillest filamentous cyanobacterium known to date,which comprises not only Chl a, but also Chl f.
The pigment composition wasdetermined 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 fto Chl a depends on cultivation conditions. Chl f was shown to be equal to12.5, 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 undetectablelevels in cells cultivated under white light. The ratio of carotenoids was alsoreduced and the total pigment content was also decreased in cells cultivatedunder white light. In this way, cells are assumed to adapt their pigmentcomposition to utilize ambient light in the most effective way: by accumulatingChl 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. Evenso, finest culture conditions as well as Chl f functions in H.
hongdechloris are not yet studied. The contrivanceof alteration of the pigment apparatus is also unclear. KC1 strain, in2011, Chl f was revealed in a unicellular cyanobacterium, strain KC1, from thefresh water Biwa Lake in Japan, Shiga Prefecture. Cells were cultured under severalradiance conditions: under white or far red light (740 nm). In both cases,pigment investigation was led by normal phase HPLC on silica gel. In cellsgrown under white light, a prevalence of Chl.a was found, whereas Chl a, andChl f were present as minor pigments.
At the same time, Chl f? and Pheo f werenot found, as in the case of other cyanobacteria. only cells grown under FRLillumination had Chl f as a minor pigment. The function of Chl f in thesecyanobacterial cells is still undetermined. Chl f may function not as a RC orelectron transfer chain intermediary, but as a light harvesting antennacomponent. One of the key features of a cyanobacterium capable of photoacclimation and growth under FRL is the presence of a cluster comprising of 21genes coding photosynthetic proteins and specifically expressed under FRL. Itis to be noted that the substitution of the electron donor methyl group CH3in ring I of Chl a by the electron acceptor formyl group CHO of Chl f causes ashift of the Qy band to longer wavelength as well as its increase, and a short wavelengthshift of the Soret band together with its reduction . Similar effects areobserved for Chl d, whose vinyl group is exchanged by a formyl group in ringII. Broadening of the absorption band by pigments capable of effectivephotosynthesis up to 750 nm is feasible, since light intensity in the 700-750nm region is not decreased much even at the water depth of 1 m.
(S.I. Allakhverdie et al. August 2015).