| This study investigated the site of ATP utilization in the signal transduction pathway of bacterial chemotaxis and localized the point of convergence of a methylation-independent system of chemotaxis with the methylation-dependent system. The identity of the signal originating from the phosphotransferase system was investigated by substituting the fructose-inducible HPr-like protein FPr for HPr in transport and chemotaxis. In addition, a novel chemoattractant, glycerol, was identified for Salmonella typhimurium. Histidine-auxotrophic S. typhimurium strains ST23 (hisF) and ST171 (hisF cheB) were depleted for ATP. The times required for the bacteria to adapt to a step increase in serine, phenol, or benzoate were similar in cells depleted of ATP and in cells with normal levels of ATP. This established that ATP was not required for the chemotactic signal to cross the inner membrane or for adaptation to the transmembrane signal to occur. The point of convergence of a methylation-independent chemotaxis system (chemotaxis to sugars transported by the phosphoenolpyruvate-energized phosphotransferase (PTS) chemotaxis system) with the methylation-dependent chemotaxis system was localized to the CheA and CheW proteins. A strain ( E. coli HCB661) containing the CheA, CheW, and CheY proteins in addition to a functional flagellar motor and switch and PTS system demonstrated a response to the sugar mannose in a tethered-cell assay. However, the response was inverted (increased tumbling instead of decreased tumbling). Strains containing the CheY protein (HCB627), the CheA and CheY proteins (HCB673), or the CheW and CheY proteins (HCB628) did not show any response to mannose. The identity of the chemotactic signal originating from the PTS is unknown. Chemotaxis wild-type S. typhimurium ST23 (hisF), LJ2046 (ptsH6), and LJ2028 (ptsH6 fruR::Tn10, constitutively expressing FPr) were tested for transport (fermentation) of fructose, glucose, mannose, mannitol, and N-acetylglucosamine. ST23 and LJ2028 were positive for all sugars tested while LJ2046 was positive only for fructose. Chemotaxis in LJ2028 as measured on minimal media semi-soft swarm plates was 70% of chemotaxis in ST23 while LJ2046 swarm diameters were 20% of ST23 (except for fructose which was 60%). Thus FPr not only restored PTS transport but also PTS chemotaxis in S. typhimurium HPr mutants. |
