The effect of gamma-ray irradiation on the Mn(ii) speciation in Deinococcus radioduransand the potential role of Mn(ii)-orthophosphates

D. radioduransaccumulates large quantities of Mn(ii), which is believed to form low molecular weight complexes with phosphate and metabolites that protect D. radioduransfrom radiation damage. The concentration of Mn(ii) species in D. radioduransduring the exponential and stationary phase was determined using high-field EPR and biochemical techniques. In the exponential growth phase cells a large fraction of the manganese was in the form of Mn(ii)-orthophosphate complexes. By contrast, the intracellular concentration of these compounds in stationary phase cells was less than 16 mu M, while that of Mn superoxide dismutase was 320 mu M and that of another, yet unidentified, Mn(ii) protein was 250 mu M. Stationary cells were found to be equally resistant to irradiation as the exponential cells in spite of having significant lower Mn(ii)-orthophosphate concentrations. Gamma irradiation induced no changes in the Mn(ii) speciation. During stationary growth phase D. radioduransfavours the production of the two Mn-proteins over low molecular weight complexes suggesting that the latter were not essential for radio-resistance at this stage of growth.