Functions Of Feo System In Manganese And Iron Transport And Oxidative Stress-resistance Of Deinococcus Radiodurans

Deinococcus radiodurans is an extreme microorganism which is extremely resistant to stresses including ionizing radiation,ultraviolet light,desiccation and oxidants.A high intracellular Mn/Fe ratio is correlated with the resistance to oxidative stress in D.radiodurans.Maintenance of Mn/Fe homeostas is plays an important role in both normal physiology and cell resistanceof D.radiodurans.In this thesis,we focused on the manganese and iron transport systems in D.radiodurans.We identified the Feo system and investigated its functions in D.radiodurans.The main results are as follows:1.We indentifed a Feo system in D.radiodurans,which consists of three proteins-FeoA(DR1220),FeoB(DR1219)and FeoC(DR1218).Feo were encoded by three genes that located in one co-transcribed operon.DR1219 was located in cell membrane as demonstrated by fluorescence labelling analysis.The mutant Mt-Feo displayed a significantly decreased level of intracellular manganese and iron,and also showed decreased cell sensitivity to manganese and iron ion compared with the wild type strain.These results indicated that Feo is a potential manganese and ferrous iron transporter.The expression level of other Mn-dependent and Fe-dependent transport genes was up-regulated significantly in the mutant Mt-Feo compared to the wild type,suggesting that Feo and other metal ions transport proteins made up the transport system of manganese and ferrous ions in D.radioduras.2.We studied the function of Feo in resistance of D.radioduran.The mutant Mt-Feo displayed lower resistance to hydrogen peroxide compared with the wild type strain.And the mutation of Feo led to significant accumulation of reactive oxygen species(ROS)and decreased activity of SOD.The expression level of Feo operon was up-regulated significantly under hydrogen peroxide stress in the wild type strain.These results suggested that under the oxidative stress,Feo systerm might contribute to the maintenance of Mn/Fe homeostasis and cell protection against ROS through its preference for manganese or iron transport.Thus,Feo system was involved in the transport of manganese and iron ions,as well as oxidative stress-resistance in D.radiodurans.The results provided a basis for further research on the mechanism of Feo and cellular resistance of D.radiodurans under oxidative stress.