Elucidation of a PTS-carbohydrate chemotactic signal pathway in Escherichia coli using a time-resolved behavioral assay

Chemotaxis of Escherichia coli toward phosphotransferase systems (PTSs)- ca rbohydrates requires phosphoenolpyruvate-dependent PTSs as well as the chem otaxis response regulator CheY and its kinase, CheA. Responses initiated by flash photorelease of a PTS substrates D-glucose and its nonmetabolizable analog methyl ar-D-glucopyranoside were measured with 33-ms time resolution using computer-assisted motion analysis. This, together with chemotactic m utants, has allowed us to map out and characterize the PTS chemotactic sign al pathway. The responses were absent in mutants lacking the general PTS en zymes EI or HPr, elevated in PTS transport mutants, retarded in mutants lac king CheZ, a catalyst of CheY autodephosphorylation, and severely reduced i n mutants with impaired methyl-accepting chemotaxis protein (MCP) signaling activity. Response kinetics were comparable to those triggered by MCP attr actant Ligands over most of the response range, the most rapid being 11.7 /- 3.1 s(-1). The response threshold was <10 nM for glucose. Responses to m ethyl alpha-D-glucopyranoside had a higher threshold, commensurate with a l ower PTS affinity, but were otherwise kinetically indistinguishable. These facts provide evidence for a single pathway in which the PTS chemotactic si gnal is relayed rapidly to MCP-CheW-CheA signaling complexes that effect su bsequent amplification and slower CheY dephosphorylation. The high sensitiv ity indicates that this signal is generated by transport-induced dephosphor ylation of the PTS rather than phosphoenolpyruvate consumption.