Garrity L F, Schiel S L, Merrill R, Reizer J, Saier M H, Ordal G W
Department of Biochemistry, Colleges of Medicine and of Liberal Arts and Sciences, University of Illinois, Urbana, Illinois 61801, USA.
J Bacteriol. 1998 Sep;180(17):4475-80. doi: 10.1128/JB.180.17.4475-4480.1998.
The phosphoenolpyruvate-dependent phosphotransferase system (PTS) plays a major role in the ability of Escherichia coli to migrate toward PTS carbohydrates. The present study establishes that chemotaxis toward PTS substrates in Bacillus subtilis is mediated by the PTS as well as by a methyl-accepting chemotaxis protein (MCP). As for E. coli, a B. subtilis ptsH null mutant is severely deficient in chemotaxis toward most PTS carbohydrates. Tethering analysis revealed that this mutant does respond normally to the stepwise addition of a PTS substrate (positive stimulus) but fails to respond normally to the stepwise removal of such a substrate (negative stimulus). An mcpC null mutant showed no response to the stepwise addition or removal of D-glucose or D-mannitol, both of which are PTS substrates. Therefore, in contrast to E. coli PTS carbohydrate chemotaxis, B. subtilis PTS carbohydrate chemotaxis is mediated by both MCPs and the PTS; the response to positive stimulus is primarily McpC mediated, while the duration or magnitude of the response to negative PTS carbohydrate stimulus is greatly influenced by components of the PTS and McpC. In the case of the PTS substrate D-glucose, the response to negative stimulus is also partially mediated by McpA. Finally, we show that B. subtilis EnzymeI-P has the ability to inhibit B. subtilis CheA autophosphorylation in vitro. We hypothesize that chemotaxis in the spatial gradient of the capillary assay may result from a combination of a transient increase in the intracellular concentration of EnzymeI-P and a decrease in the concentration of carbohydrate-associated McpC as the cell moves down the carbohydrate concentration gradient. Both events appear to contribute to inhibition of CheA activity that increases the tendency of the bacteria to tumble. In the case of D-glucose, a decrease in D-glucose-associated McpA may also contribute to the inhibition of CheA. This bias on the otherwise random walk allows net migration, or chemotaxis, to occur.
磷酸烯醇丙酮酸依赖性磷酸转移酶系统（PTS）在大肠杆菌向PTS糖类迁移的能力中起主要作用。本研究证实，枯草芽孢杆菌中对PTS底物的趋化作用是由PTS以及甲基接受趋化蛋白（MCP）介导的。与大肠杆菌一样，枯草芽孢杆菌ptsH基因敲除突变体在对大多数PTS糖类的趋化作用上严重缺陷。系留分析表明，该突变体对PTS底物的逐步添加（正向刺激）反应正常，但对这种底物的逐步去除（负向刺激）反应不正常。mcpC基因敲除突变体对D - 葡萄糖或D - 甘露醇（两者均为PTS底物）的逐步添加或去除均无反应。因此，与大肠杆菌的PTS糖类趋化作用不同，枯草芽孢杆菌的PTS糖类趋化作用由MCP和PTS共同介导；对正向刺激的反应主要由McpC介导，而对PTS糖类负向刺激的反应持续时间或幅度则受PTS和McpC组分的极大影响。对于PTS底物D - 葡萄糖，对负向刺激的反应也部分由McpA介导。最后，我们表明枯草芽孢杆菌的酶I - P在体外具有抑制枯草芽孢杆菌CheA自磷酸化的能力。我们推测，毛细管试验空间梯度中的趋化作用可能是由于细胞沿糖类浓度梯度向下移动时，酶I - P细胞内浓度的短暂增加和与糖类相关的McpC浓度降低共同作用的结果。这两个事件似乎都有助于抑制CheA活性，从而增加细菌翻滚的倾向。对于D - 葡萄糖，与D - 葡萄糖相关的McpA的减少也可能有助于抑制CheA。这种对原本随机游动的偏向使得净迁移或趋化作用得以发生。
