in energy metabolism, c. tepidum relies on light reactions to produce energy (nadph and nadh) because the pathways typically responsible for energy production (oxidative pentose phosphate pathway and normal tca cycle) are only partly functional. photons absorbed from the light are used to produce nadph and nadh, the cofactors of energy metabolism. c. tepidum also generates energy in the form of atp using the proton motive force derived from sulfide oxidation. energy production from both sulfide oxidation and photon absorption via bacteriochlorophylls. nitrogen fixation the majority of green sulfur bacteria are diazotrophs: they can reduce nitrogen to ammonia which is then used to synthesize amino acids. nitrogen fixation among green sulfur bacteria is generally typical of an anoxygenic phototroph, and requires the presence of light. green sulfur bacteria exhibit activity from a type-1 secretion system and a ferredoxin-nadp+ oxidoreductase to generate reduced iron, a trait that evolved to support nitrogen fixation. like purple sulfur bacteria, they can regulate the activity of nitrogenase post-translationally in response to ammonia concentrations. their possession of nif genes, even though evolutionarily distinct, may suggest their nitrogen fixation abilities arose in two different events or through a shared very distant ancestor. examples of green sulfur bacteria capable of nitrogen fixation include the genus chlorobium and pelodictyon, excluding p. phaeoclathratiforme. prosthecochloris aestuarii and chloroherpeton thalassium also fall into this category. their n2 fixation is widespread and plays an important role in overall nitrogen availability for ecosystems. green sulfur bacteria living in coral reefs, such as prosthecochloris, are crucial in generating available nitrogen in the already nutrient-limited environment.