FERRIC ION AS PHOTORECEPTOR OF PHOTO‐ PHOBOTAXIS IN NON‐PIGMENTED RHODOSPIRILLUM RUBRUM

Abstract

Abstract— Rhodospirillum rubrum cultivated aerobically and containing no detectable bacteriochloro‐phyll assembled in their phobotactic response into a spot of blue and near UV light. The shape of the action spectrum for the phenomenon was similar to that of the absorption spectrum of ferric ion in aqueous solution. The photophobotactic response was not observed in media containing no ferric ion. Increasing concentration of the ion in the media resulted in an increasing degree of their photophobotactic response. Ferrous ion could not be substituted for ferric ion unless its autooxidation in medium was allowed.In addition to ferric ion, existence of appropriate anion, by which photoreduction of ferric ion took place efficiently, was necessary to induce an appreciable photophobotactic response. This suggested that the apparent photophobotaxis was, strictly speaking, chemophobotaxis induced by a photochemical product of ferric complex in medium.