The Photosystem of Green Sulfur Bacteria

The second group of photosynthetic organisms that possesses a FeS-type photosystem is green sulfur bacteria (GSB). These organisms comprise a phylogentic group of photosynthetic gram-negative bacteria [42]- In 1887, Winogradsky -43] suggested naming the group of organisms that can oxidize hydrogen sulfide into sulfur "Schwefelbacterien" (Engl. sulfur bacteria). The distinct pigments found in green sulfur bacteria pointed for a long time at a distinct photosynthetic apparatus; but it was only when biochemical and electron microscopy studies linked the pig ments with the membranous vesicles that the true uniqueness of green sulfur bacterial photosynthesis became apparent -44] - Chlorosomes are the dominating light-harvesting systems in GSB and contain hundreds of thousands of BChl c,d and/or e molecules. Chlorosomes are enclosed by a unilayer membrane facing the cytoplasm and an array of BChl a containing proteins, which constitute the baseplate. The baseplate energetically couples the chlorosomes to the reaction center via the Fenna-Matthews-Olson (FMO)-protein. The FMO-proteins form trimers that are very tightly linked to the FeS-type RC. The RC of green sulfur bacteria has been reviewed in detail [45].

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