Abstract
The baseplate subantenna in chlorosomes of green anoxygenic photosynthetic bacteria, belonging to the families Chloroflexaceae and Chlorobiaceae, is known to represent a complex of bacteriochlorophyll (BChl) a with the ~6 kDa CsmA proteins. Earlier, we showed the existence of a similar BChl a subantenna in chlorosomes of the photosynthetic green bacterium Oscillochloris trichoides, member of Oscillochloridaceae, the third family of green photosynthetic bacteria. However, this BChl a subantenna was not visually identified in absorption spectra of isolated Osc. trichoides chlorosomes in contrast to those of Chloroflexaceae and Chlorobiaceae. In this work, using room and low-temperature absorbance and fluorescence spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of alkaline-treated and untreated chlorosomes of Osc. trichoides, we showed that the baseplate BChl a subantenna does exist in Oscillochloridaceae chlorosomes as a complex of BChl a with the 5.7 kDa CsmA protein. The present results support the idea that the baseplate subantenna, representing a complex of BChl a with a ~6 kDa CsmA protein, is a universal interface between the BChl c subantenna of chlorosomes and the nearest light-harvesting BChl a subantenna in all three known families of green anoxygenic photosynthetic bacteria.
Highlights
Green anoxygenic bacteria comprise three phylogenetically unrelated families of photosynthetic bacteria: green sulfur bacteria and green filamentous bacteria [1,2,3]
In 2000, the genus Oscillochloris was excluded from the family Chloroflexaceae, and a new family Oscillochloridaceae was proposed based on phylogenetic data and unique physiological, biochemical, and chemotaxonomical properties [3]
It was shown that the purified chlorosomes of Osc. trichoides exhibited a single peak of BChl c at 750 nm in the near-infrared region of the absorption spectra at room temperature [35]
Summary
Green anoxygenic bacteria comprise three phylogenetically unrelated families of photosynthetic bacteria: green sulfur bacteria (family Chlorobiaceae) and green filamentous bacteria (families Chloroflexaceae and Oscillochloridaceae) [1,2,3]. The idea of association of BChl a with protein in chlorosomes of Osc. trichoides was probed by roomand low-temperature absorbance and fluorescence spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of alkaline-treated and untreated chlorosomes.
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