Biochemical and spectroscopic analysis of photosynthetic complexes from Gemmatimonas phototrophica

Marko Dacheva,b, Roman Sobotkaa,b, David Kaftana,b, Peter Koníkb, Václav Šloufb, Zdeno Gardianc, David Bínac, Michal Koblížeka,b
aInstitute of Microbiology CAS, Center Algatech, 37981 Třeboň, Czech Republic; bUniv of South Bohemia, Faculty of Science, 370 05 Č. Budějovice, Czech Rep; cBiology Center CAS, IPMB, Branišovská 31, 370 05 Č. Budějovice, Czech Rep

G. phototrophica is a recently discovered phototrophic bacterium belonging to a rarely studied phylum Gemmatimonadetes [1,2]. Grown under semi-aerobic conditions, it contains a unique light-harvesting (LH) antenna complex. The complex was purified using an anion-exchange chromatography and size-exclusion chromatography. The complex shows two infrared absorption bands at 820 and 866 nm. Using the femto-second transient absorption spectroscopy, we determined that the excitation transfer rate between the absorption bands in the near infra region to be 2 ps. The complex contained a novel unknown carotenoid absorbing at 500 nm. Fluorescence excitation spectra documented that this carotenoid has 75% energy transfer efficiency to bacteriochlorophyll. The single cell particle analysis revealed an unusual large circular structure of the photosynthetic complex which consists from two concentric rings around the type-2 reaction center. The analysis of the protein composition done by 2D gel electrophoresis and mass spectrometry suggests that the both rings are formed from the same proteins. There are no LH2 genes present in the genome [2]. The unique organization and properties of this LH complex may provide new insights in bacterial photosynthesis.

References

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[2] Zeng Y-H, Selyanin V, Lukes M, Dean J, Kaftan D, Feng F, Koblizek M. Characterization of microaerophilic bacteriochlorophyll a-contatining bacterium Gemmatimonas phototrophica sp.nov., and emended descriptions of the genus Gemmatimonas and Gemmatimonas aurantiaca. Int J Syst Evol Microbiol 2015, 65, 2410-2419.