What is "photofermentation"

n. fermentation that only proceeds in the presence of light; especially a process of producing hydrogen. Unlike biophotolysis in which hydrogen is produced from water, photofermentation produces hydrogen from organic substrates.

Photofermentation is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group of photosynthetic bacteria by a series of biochemical reactions involving three steps similar to anaerobic conversion. Photofermentation differs from dark fermentation because it only proceeds in the presence of light.

For example photo-fermentation with Rhodobacter sphaeroides SH2C (or many other purple non-sulfur bacteria) can be employed to convert small molecular fatty acids into hydrogen and other products.