Chlorobaculum tepidum , a model photosynthetic green sulfur bacterium, possesses a variety of bacteriochlorophyll c pigments in light‐harvesting organelles called chlorosomes (background; TEM of negatively stained chlorosomes). Bacteriochlorophyll has a 3‐1‐hydroxyethyl group that produces a chiral center with R‐ or S‐stereochemistry. C. tepidum adapts to low‐light by regulating the activities of the BchF and BchV hydratases and thus the pigment composition of the chlorosome. For details, see the article by Harada et al . on pp. 1184–1198 of this issue.