Characterization of the Rhizobium (Sinorhizobium) meliloti high- and low-affinity phosphate uptake systems
Characterization of the Rhizobium (Sinorhizobium) meliloti high- and low-affinity phosphate uptake systems
复制标题
苜蓿根瘤菌高和低亲和力磷酸盐吸收系统的表征
DOI：
10.1128/jb.179.23.7226-7232.1997
复制
发表时间：
1997
影响因子：
3.2
通讯作者：
T. Finan
中科院分区：
文献类型：
--
作者：
R. Voegele;S. Bardin;T. Finan
Genetic studies have suggested that Rhizobium (Sinorhizobium) meliloti contains two distinct phosphate (Pi) transport systems, encoded by the phoCDET genes and the orfA-pit genes, respectively. Here we present data which show that the ABC-type PhoCDET system has a high affinity for Pi (Km, 0.2 microM) and that Pi uptake by this system is severely inhibited by phosphonates. This high-affinity uptake system was induced under Pi-limiting conditions and was repressed in the presence of excess Pi. Uptake via the OrfA-Pit system was examined in (i) a phoC mutant which showed increased expression of the orfA-pit genes as a result of a promoter-up mutation and (ii) a phoB mutant (PhoB is required for phoCDET expression). Pi uptake in both strains exhibited saturation kinetics (Km, 1 to 2 microM) and was not inhibited by phosphonates. This uptake system was active in wild-type cells grown with excess Pi and appeared to be repressed when the cells were starved for Pi. Thus, our biochemical data show that the OrfA-Pit and PhoCDET uptake systems are differentially expressed depending on the state of the cell with respect to phosphate availability.
