Unusual resistance to ultraviolet light in dark phase of blue-green bacterium Anacystis nidulans

Abstract

THE role of visible light in the repair of ultraviolet light-induced damage has been extensively studied in various organisms¹. In blue-green bacteria, photoreactivation has been found to be extremely efficient². Indeed, in these organisms, which generally need light as a growth factor, the presence of an efficient photoreactivation mechanism hinders the detection of alternative repair steps which may be present. In spite of this difficulty, however, the existence of light-independent (that is, dark) repair has been observed in blue-green bacteria as suggested by the isolation of mutants with altered ultraviolet light sensitivity^3,4. Here we report an interesting observation suggesting the presence of a very efficient repair system against damage induced by ultraviolet light (254 nm) in an obligate photo-autotrophic blue-green bacterium Anacystis nidulans. We show that this repair system is either inhibited or less effective under aerobic conditions in the presence of light.