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.