Jacobs M H, van der Heide T, Tolner B, Driessen A J, Konings W N
Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
Mol Microbiol. 1995 Nov;18(4):641-7. doi: 10.1111/j.1365-2958.1995.mmi_18040641.x.
Rhodobacter sphaeroides is chemotactic to glutamate and most other amino acids. In Escherichia coli, chemotaxis involves a membrane-bound sensor that either binds the amino acid directly or interacts with the binding protein loaded with the amino acid. In R. sphaeroides, chemotaxis is thought to require both the uptake and the metabolism of the amino acid. Glutamate is accumulated by the cells via a binding protein-dependent system. To determine the role of the binding protein and transport in glutamate taxis, mutants were created by Tn5 insertion mutagenesis and selected for growth in the presence of the toxic glutamine analogue gamma-glutamyl-hydrazide. One of the mutants, R. sphaeroides MJ7, was defective in glutamate uptake but showed wild-type levels of binding protein. The mutant showed no chemotactic response to glutamate. Both glutamate uptake and chemotaxis were recovered when the gltP gene, coding for the H(+)-linked glutamate carrier of E. coli, was expressed in R. sphaeroides MJ7. It is concluded that the chemotactic response to glutamate strictly requires uptake of glutamate, supporting the view that intracellular metabolism is needed for chemotaxis in R. sphaeroides.
球形红细菌对谷氨酸及大多数其他氨基酸具有趋化性。在大肠杆菌中，趋化作用涉及一种膜结合传感器，该传感器要么直接结合氨基酸，要么与负载有氨基酸的结合蛋白相互作用。在球形红细菌中，趋化作用被认为既需要氨基酸的摄取，也需要其代谢。谷氨酸通过一种依赖结合蛋白的系统被细胞积累。为了确定结合蛋白和转运在谷氨酸趋化中的作用，通过Tn5插入诱变创建了突变体，并在有毒的谷氨酰胺类似物γ-谷氨酰肼存在的情况下选择用于生长。其中一个突变体，球形红细菌MJ7，在谷氨酸摄取方面存在缺陷，但显示出野生型水平的结合蛋白。该突变体对谷氨酸没有趋化反应。当编码大肠杆菌H(+)连接的谷氨酸载体的gltP基因在球形红细菌MJ7中表达时，谷氨酸摄取和趋化作用都恢复了。结论是，对谷氨酸的趋化反应严格需要谷氨酸的摄取，这支持了球形红细菌趋化需要细胞内代谢的观点。
