The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic c...The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is abso-lutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5α strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc-curred only at a certain depth under the surface of M63- 0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentra-tions, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regu-lated by oxygen concentration.展开更多
基金This work was supported by the National Key Basic Research(973)Program of the Ministry of Science and Technology of China(Grant No.2001CB 108903)China-Ireland International Collabo ration Program of the Ministry of Science and Technology of China and Science Foundation of Ireland(Grant No.CI-2003-07)the National Natural Science Foundation of China(Grant No.39925017).
文摘The Sinorhizobium meliloti C4-dicarboxylate transport (Dct) system is essential for symbiotic nitrogen fixation. The dctA gene, encoding the C4-dicarboxylate per-mease, is expressed in both free living and symbiotic cells. But in free living cells expression of dctD and dctB is abso-lutely required for the expression of dctA. In this study, in order to investigate the effect of oxygen concentration on the induction of Dct system, E. coli DH5α strain which carries the plasmid-encoded dctABD operon was used in tube assays. It was found that the specific induction of Dct system oc-curred only at a certain depth under the surface of M63- 0.6% agar media, suggesting that Dct system could respond to oxygen concentration during succinate-induced expression. Furthermore, when measured at different oxygen concentra-tions, the highest expression level was observed at oxygen concentration of 2%. Thus, we predict that in addition to dicarboxylates, the induction of Dct system may also regu-lated by oxygen concentration.
