These antibiotics include&colon; herbicolin, pantocins, phenazine and many more. When the bacteria are exposed to ammonia, darkness, and phenazine methosulfate, nitrogen fixation stops. The only known biological sources of phenazine compounds are bacterial in nature. It reacts with nitrobenzene to produce phenazine in the Wohl-Aue reaction. Sequential modifications then lead to a variety of phenazine with differing biological activities. Clofazimine is a phenazine dye and believed to work by interfering with DNA. "Pseudomonas fluorescens" produces phenazine, phenazine carboxylic acid, 2,4-diacetylphloroglucinol and the MRSA-active antibiotic mupirocin. Phenazine biosynthesis branches off the shikimic acid pathway at a point subsequent to chorismic acid. Phenazine crystallizes in yellow needles, which are only sparingly soluble in alcohol. Classically phenazine are prepared by the reaction of nitrobenzene and aniline in the Wohl-Aue reaction.