A chlorosome is a photosynthetic antenna complex found in green sulfur bacteria (GSB) and many green non-sulfur bacteria (GNsB), together known as green bacteria. They differ from other antenna complexes by their large size and lack of protein matrix supporting the photosynthetic pigments. Green sulfur bacteria are a group of organisms that generally live in extremely low-light environments, such as at depths of 100 metres in the Black Sea. The ability to capture light energy and rapidly deliver it to where it needs to go is essential to these bacteria, some of which see only a few photons of light per chlorophyll per day. To achieve this, the bacteria contain chlorosome structures, which contain up to 250,000 chlorophyll molecules. Chlorosomes are ellipsoidal bodies, in GSB their length varies from 100 to 200 nm, width of 50-100 nm and height of 15 – 30 nm, in GNsB the chlorosomes are somewhat smaller. Structure Chlorosome shape can vary between species, with some species containing ellipsoidal shaped chlorosomes and others containing conical or irregular shaped chlorosomes. Inside green sulfur bacteria, the chlorosomes are attached to type-I reaction centers in the cell membrane via FMO-proteins and a chlorosome baseplate composed of CsmA proteins. Filamentous anoxygenic phototrophs of the phylum Chloroflexota lack the FMO complex, but instead use a protein complex called B808-866. Unlike the FMO proteins in green sulfur bacteria, B808-866 proteins are embedded in the cytoplasmic membrane and surround type-II reaction centers, providing the link between the reaction centers and the baseplate. The composition of the chlorosomes is mostly bacteriochlorophyll (BChl) with small amounts of carotenoids and quinones surrounded by a galactolipid monolayer. In Chlorobi, chlorosome monolayers can contain up to eleven different proteins. The proteins of Chlorobi are the ones currently best understood in terms of structure and function. These proteins are named CsmA through CsmF, CsmH through CsmK, and CsmX. Other Csm proteins with different letter suffixes can be found in Chloroflexota and Ca. "Chloracidobacterium". Within the chlorosome, the thousands of BChl pigment molecules have the ability to self assemble with each other, meaning they do not interact with protein scaffolding complexes for assembly. These pigments self assemble in lamellar structures about 10-30 nm wide. Organization of the light harvesting pigments Bacteriochlorophyll and carotenoids are two molecules responsible for harvesting light energy. Current models of the organization of bacteriochlorophyll and carotenoids (the main constituents) inside the chlorosomes have put them in