Molecular analysis of phosphate taxis in bacteria.

a)我们分离到了组成型碱性磷酸酶（AP）的铜绿假单胞菌PAO1和阴沟假单胞菌IFO3320突变体。这些突变体的遗传分析表明，突变位于后操纵子。在P_i过量的条件下，铜绿假单胞菌突变株对P_i表现出趋化反应。这些结果表明，Pst对铜绿假单胞菌中P_i趋向性的表达具有负向控制作用。即使在P_i限制的条件下，e.c eroacae AP组成型突变体对P_i也没有趋化反应。这些结果表明，阴沟肠杆菌的Pst系统是P_i化学接受所必需的。b)由于没有方便的方法选择P_i缺陷突变体，我们决定以编码氨基酸MCP的pctA基因为探针，克隆一个编码P_i趋向性MCP的基因。在pcta侧区发现了两个MCP基因pctB和pctC。遗传分析显示PctB和PctC分别参与7个和2个l -氨基酸的趋化性。铜绿假单胞菌敲除pctA、pctB和pctC的突变体表现出P_i趋向性，表明3种MCPs不参与P_i趋向性。我们又分离出七个与pctA基因杂交的DNA片段。对这些碎片的调查正在进行中。

a) We isolated P.aeruginosa PAO1 and E.cloacae IFO3320 mutants which constitutively produced alkaline phospgatase (AP). Genetic analysis of these mutants revealed that mutations located in the pst operon. P.aeruginosa mutant strains showed chemotactic response to P_i under conditions of P_i excess. These results indicate that Pst negatively controls the expression of P_i taxis in P.aeruginosa. E.cloacae AP constitutive mutants did not show chemotactic response to P_i even under conditions of P_i limitations. These results suggest that the E.cloacae Pst system is required for P_i chemoreception. b) Since there is no convenient method for selecting P_i defective mutants, we decided to clone a gene encoding a MCP for P_i taxis by using the pctA gene, which encodes a MCP for amino acids, as probe. Two MCP genes (termed pctB and pctC) were found in the pctA-flanking region. Genetic analysis revealed that PctB and PctC were involved in chemotaxis to seven and two L-amino acids, respectively. The P.aeruginosa knock-out mutant of pctA,pctB and pctC showed P_i taxis, suggestig that three MCPs were not involved in P_i taxis. We have isolated seven more DNA fragments hybridized with the pctA gene. Investigation of these fragments is under way.