Radioprotection in E. coli by an agent from M. radiodurans

The effect of gamma-ray irradiation on the Mn(II) speciation in Deinococcus radiodurans and the potential role of Mn(II)-orthophosphates

D. radiodurans accumulates large quantities of Mn(II), which is believed to form low molecular weight complexes with phosphate and metabolites that protect D. radiodurans from radiation damage. The concentration of Mn(II) species in D. radiodurans during 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 μM, while that of Mn superoxide dismutase was 320 μM and that of another, yet unidentified, Mn(II) protein was 250 μM. 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. radiodurans favours 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.

Extreme resistance of bdelloid rotifers to ionizing radiation

Rotifers of class Bdelloidea are common invertebrate animals with highly unusual characteristics, including apparently obligate asexuality, the ability to resume reproduction after desiccation at any life stage, and a paucity of transposable genetic elements of types not prone to horizontal transmission. We find that bdelloids are also extraordinarily resistant to ionizing radiation (IR). Reproduction of the bdelloids Adineta vaga and Philodina roseola is much more resistant to IR than that of Euchlanis dilatata, a rotifer belonging to the desiccation-intolerant and facultatively sexual class Monogononta, and all other animals for which we have found relevant data. By analogy with the desiccation- and radiation-resistant bacterium Deinococcus radiodurans, we suggest that the extraordinary radiation resistance of bdelloid rotifers is a consequence of their evolutionary adaptation to survive episodes of desiccation encountered in their characteristic habitats and that the damage incurred in such episodes includes DNA breakage that is repaired upon rehydration. Such breakage and repair may have maintained bdelloid chromosomes as colinear pairs and kept the load of transposable genetic elements low and may also have contributed to the success of bdelloid rotifers in avoiding the early extinction suffered by most asexuals.