Lumazine is a fluorescent pteridine occurring naturally in plants (Brassica juncea), insects (Formica polyctena) and the sea sponge Corallistes fulvodesmus, recently reviewed by Brimble and co-workers, University of Auckland, New Zealand. Lumazine is a photosensitizing agent, generating a singlet oxygen on UV irradiation. Lumazine is bactericidal to Methanobacterium thermoautotrophisum strain Marburg and is a selective inhibitor of methanogenesis used to improve the hydrogen production in microbial electrolysis cells.