The in Vivo Association of Manganese With the Chromosome of Micrococcus Radiodurans

Abstract —Extremely high levels of paramagnetic manganese (Mn 2+ ) which quench phosphorescent reactions have been found to inhibit the formation of thymine‐containing dimers in M. radiodurans . Lowering the concentration of Mn 2+ in the culture medium resulted in a lower intracellular concentration of Mn 2+ , an increase in the UV‐sensitivity of this bacterium, and a larger photochemical yield of thymine‐containing dimers. High levels of paramagnetic Mn 2+ were not found in other test organisms which are more sensitive to UV‐irradiation. One interpretation of our data is that in Micrococcus radiodurans Mn 2+ may bind to the chromosome and thereby reduce the photochemical yield of thymine‐containing dimers.