CC BY
13B-P-10
BIOMEDICAL PHOTONICS
Raman study of the cyanobacterium Synechocystis sp. PCC 6803 mutants
deficient in phycobiliproteins
E. Perevedentseva1, E. Muronets2, N. Melnik1, A. Karmenyan3, I. Elanskaya2
1- P.N. Lebedev Physical Institute of Rus. Acad. Sci., Moscow, Russia 2- Biological Dept of Moscow State University, Moscow, Russia 3- Department of Physics, National Dong Hwa University, Hualien, Taiwan perevedencevaev@lebedev. ru
Cyanobacteria are the model organisms for studying photosynthesis; their applications in ecotoxicological analysis are also suggested. Raman spectroscopy allows analyzing and comparison of chemical composition of the cyanobacteria strains and studying of the state and conformation of the molecules which participate in the living processes of cyanobacteria. In order to collect spectral information about different structural components of cyanobacterial cells, in the present work Raman spectra of the cyanobacterium Synechocystis sp. PCC 6803 mutants deficient in phycobiliproteins, which are parts of the light harvesting antenna of cyanobacteria, were measured and analyzed. The wild type of Synechocystis, CK mutant, and PAL mutant were grown for 4-5 days in liquid BG-11 medium at 30oC and white light intensity of 40 mmol photons m-2 s-1. The suspension of cyanobacteria in growth medium was placed into the quartz cuvette with a thickness 2 mm and the cuvette was positioned on the microscopic stage of InVia Raman spectrometer (Renishaw, GB) equipped with lasers with 785 nm and 1064 nm wavelengths. For the spectra acquisition the laser beam was focused inside the cuvette via objective N Plan 50/0.50 (Leica, Germany) with long working distance.
Raman shift, cm
Fig. 1. Raman spectra of cyanobacteria. The most pronounced spectral lines can be attributed to carotenoids (1155 cm-1, 1519 cm-1) and phycobiliproteins (1003, 1110, 1192, 1280, 1370, 1632 cm-1), weaker lines are originated from scytonemin and its derivatives (e.g. near 1450 and 1590 cm-1) and chlorophyll (1328, 1555 cm-1) [1]
Characteristic spectra for 3 samples measured at 1064 nm excitation are shown in Fig. 1. The spectra obtained with excitation 785 nm are comparable. Clear difference in the spectra of studied samples is observed in the areas of peaks 1370 and 1632 cm-1 originated from phycobiliproteins. The function of formed by phycobiliproteins antenna complex is to absorb light and to transfer the excitation energy to the photosynthetic reaction centers. Observed results can be brought into line with the data concerning the structure of the antenna complexes of the wild type (contains both phyco-cyanin and allophycocyanin), CK (contains only allophycocyanin) and PAL (lacking both phycocyanin and allophyco-cyanin). Thus, Raman spectroscopy with excitation in near IR allows distinguishing different cyanobacterial strains and determining the origin of the difference on the biomolecular level.
[1] P. Vitek, J. Wierzchos. Microbial Ecosystems in Central Andes Extreme Environments: Biofilms, microbial mats, microbialites
and endoevaporites, (Springer), Desert biosignatures, (2020).
