Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with th...Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with the disruption of the nifA gene are reported in this study. Under a free-living state, S. meliloti nifA mutant reduces its ability to swarm on a half-solid plate. Interestingly, the AHL （Acylhomoserine lactones） contents in the nifA mutant are lower than that of the wild type during the lag phase, whereas it is reversed in the logarithmic and stationary phases. Quantitative spectrophotometric assays reveal that the total amount of extracellular proteins of the nifA mutant are lower than that of the wild type. In addition, the mutant abolishes its nodulation competitive ability during symbiosis. These findings indicate that NifA plays a regulatory role in multiple cellular processes in S. meliloti.展开更多
The moblizable plashed pBF101 carrying Tn5-nifA of E. cloacae E26 was introduced into K. oxytoca NG13 with high frequency from donor E. coli S17-1 by mating. Tn5-nifA was transposed spontaneously from PBF101 into the ...The moblizable plashed pBF101 carrying Tn5-nifA of E. cloacae E26 was introduced into K. oxytoca NG13 with high frequency from donor E. coli S17-1 by mating. Tn5-nifA was transposed spontaneously from PBF101 into the genome of NG13 with a frequency of 6 ×10-5. Strain NG1394 was obtamed by selecting KmrCms colonies,which had lost plashed PBF101 and into which transposition of Tns-nifA had occurred. The integrahon of nifA gene into the genome in NG1394 was verified by agarose gel electrophoresis (Fig. 1) and curing of plasdrid with acridine orange. The synthesis of nitrogrnase in NG1394 was not repressed by (Table 1 ). Constitutive nifA could be stably maintained in NG1394 without antibiotic selection stress. borne nitrogenase activity was detected in NG1394 at 39℃ while NG13 (wild type) competely lost the activity at 39℃ (table 2).展开更多
基金This work was supported by the National Grand Fundamental Research 973 Project (No. 2001CB108901)National Science Foundation of China (No. 30400267).
文摘Sinorhizobium meliloti nifA is important in fixing nitrogen during symbiosis. A nifA null mutant induces small white invalid nodules in the roots of host plant. The additional phenotypic alterations associated with the disruption of the nifA gene are reported in this study. Under a free-living state, S. meliloti nifA mutant reduces its ability to swarm on a half-solid plate. Interestingly, the AHL （Acylhomoserine lactones） contents in the nifA mutant are lower than that of the wild type during the lag phase, whereas it is reversed in the logarithmic and stationary phases. Quantitative spectrophotometric assays reveal that the total amount of extracellular proteins of the nifA mutant are lower than that of the wild type. In addition, the mutant abolishes its nodulation competitive ability during symbiosis. These findings indicate that NifA plays a regulatory role in multiple cellular processes in S. meliloti.
文摘The moblizable plashed pBF101 carrying Tn5-nifA of E. cloacae E26 was introduced into K. oxytoca NG13 with high frequency from donor E. coli S17-1 by mating. Tn5-nifA was transposed spontaneously from PBF101 into the genome of NG13 with a frequency of 6 ×10-5. Strain NG1394 was obtamed by selecting KmrCms colonies,which had lost plashed PBF101 and into which transposition of Tns-nifA had occurred. The integrahon of nifA gene into the genome in NG1394 was verified by agarose gel electrophoresis (Fig. 1) and curing of plasdrid with acridine orange. The synthesis of nitrogrnase in NG1394 was not repressed by (Table 1 ). Constitutive nifA could be stably maintained in NG1394 without antibiotic selection stress. borne nitrogenase activity was detected in NG1394 at 39℃ while NG13 (wild type) competely lost the activity at 39℃ (table 2).
