Figure 1. Photosynthetic apparatus of the green sulfur bacteria. In transmission electron micrographs chlorosomes are visible as ovoid structures appressed to the inner side of the cytoplasmatic membrane. The chlorosomes contain aggregated antenna bacteriochlorophylls c/d/e (forming the rod elements) and are separated from the cytoplasm by a monolayer of monogalactosyl diglyceride. The latter is thought to contain different chlorosomal proteins (CsmA, CsmB, CsmC). Chlorosomes are connected to the photosynthetic reaction centre in the cytoplasmic membrane via the small trimeric FMO proteins. Solid arrows in the reaction centre indicate the transfer of an electron which is initiated by excitation of the primary donor P840. Dashed arrows mark the transfer of excitation from antenna carotenoid and bacteriochlorophylls c/d/e towards P840. CM, cytoplasmic membrane; CW, cell wall; OM, outer membrane. Bar, 0.1 µm.

Figure 2. Schematic representation of the structure of phototrophic consortia. The consortia consist of green sulfur bacterial epibionts and a central colourless motile rod-shaped bacterium. (a) Intact consortium. Only the epibionts which are arranged in a regular fashion can be seen from the outside. (b) The central colourless bacterium (indicated in red) becomes visible when phototrophic consortia are disintegrated by squeezing them between a coverslip and a microscopic slide. Bar, 1 µm.