Phototaxis away from blue light by an Escherichia coli mutant accumulating protoporphyrin IX

The hemH gene of Escherichia coli encodes ferrochelatase (EC 4.99.1.1), the enzyme that catalyzes the last step in the production of heme, namely the synthesis of heme from protoporphyrin IX plus Fe2+. The behavioral responses to light were studied in E. coli carrying a hemH mutation. It was shown that the hemH mutant displayed a tumbling response upon illumination and a running response upon removal of the light. The most effect light to induce a tumbling response in the hemH mutant was blue light (396-450 nm). The chemotaxis machinery was needed for the light-induced tumbling response in the hemH mutant. The bacterial defect is an analog of the human inherited disease erythropoietic protoporphyria.