EXPRESSION OF THE GLTP GENE OF ESCHERICHIA-COLI IN A GLUTAMATE TRANSPORT-DEFICIENT MUTANT OF RHODOBACTER-SPHAEROIDES RESTORES CHEMOTAXIS TOGLUTAMATE

Rhodobacter sphaeroides is chemotactic to glutamate and most other ami no acids. In Escherichia coli, chemotaxis involves a membrane-bound se nsor that either binds the amino acid directly or interacts with the b inding protein loaded with the amino acid. In R. sphaeroides, chemotax is is thought to require both the uptake and the metabolism of the ami no acid. Glutamate is accumulated by the cells via a binding protein-d ependent system. To determine the role of the binding protein and tran sport in glutamate taxis, mutants were created by Tn5 insertion mutage nesis and selected for growth in the presence of the toxic glutamine a nalogue gamma-glutamyl-hydrazide. One of the mutants, R. sphaeroides M J7, was defective in glutamate uptake but showed wild-type levels of b inding protein. The mutant showed no chemotactic response to glutamate . Both glutamate uptake and chemotaxis were recovered when the gltP ge ne, coding for the H+-linked glutamate carrier of E. coli, was express ed in R. sphaeroides MJ7. It is concluded that the chemotactic respons e to glutamate strictly requires uptake of glutamate, supporting the v iew that intracellular metabolism is needed for chemotaxis in R. sphae roides.