Coproporphyrin excretion by Azorhizobium caulinodans under micro-aerobic conditions

Azorhizobium caulinodans ORS571 was found to excrete moderate amounts of a fluorescent pigment into the culture medium in response to dissolved oxygen tensions below 1.0 kPa. The pigment was identified as coproporphyrin, on t he basis of its optical and fluorescence spectra. FixLJ and fixK mutant der ivatives of ORS571 were found to excrete 25-fold higher amounts of copropor phyrin under micro-aerobic conditions than the wild type strain. These obse rvations suggest that A. caulinodans switches from an aerobic to an anaerob ic coproporphyrinogen oxidase when the dissolved oxygen tension falls below 1.0 kPa and that the fixLJ and fixK genes are involved in the regulation o f expression of the anaerobic coproporphyrinogen oxidase.