Novel concentric light harvesting antennae in Gemmatimonas phototrophica

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

Species capable of harvesting light energy using (bacterio-)chlorophyll reaction centers have been found in seven bacterial phyla. The recently described bacterium Gemmatimonas phototrophica, represents so far the only phototrophic member of the bacterial phylum Gemmatimonadetes [1,2]. It contains photosynthetic reaction centers, related to those found in purple bacteria. The electron microscopy showed that G. phototrophica contained unusually large circular photosynthetic complexes with the outer diameter of ~18 nm. The complexes had about four times larger functional cross-section than the RC-LH1 complexes in Rsp. rubrum. The single particle analysis revealed that the complexes had an unusual organization with two concentric rings around the type-2 reaction center. The rings had the fixed stoichiometry of 16 subunits in the outer, and 10 subunits in the inner ring. The whole complex contained 62.4 ± 4.7 bacteriochlorophyll a molecules. The complex has two distinct infra-red absorption bands with fixed peak area ratios and maxima at 820 and 867 nm. Using the femtosecond pump-and-probe spectroscopy we determined the excitation transfer rate between these spectral bands was ~2 ps, confirming its high efficiency.

Assuming that the photosynthesis genes in Gemmatimonadetes were originally acquired horizontally from purple bacteria [2], our data suggests that after the horizontal transfer event, the architecture of light harvesting complexes probably evolved in Gemmatimonadetes along its own individual pathway.

Figure 1. A: The photosynthetic complex from G. phototrophica, B: LH1-RC complex from Rsp. rubrum

References

[1] Y.H. Zeng, F.Y. Feng, H. Medová, J. Dean, M. Koblížek, Proc Natl Acad Sci USA 2014, 111, 7795-7800.
[2] Y.H. Zeng, V. Selyanin, M. Lukeš, J. Dean, D. Kaftan, F. Feng, M. Koblížek, Int J Syst Evol Microbiol 2015, 65,2410-2419.