METABOLISM IS REQUIRED FOR CHEMOTAXIS TO SUGARS IN RHODOBACTER-SPHAEROIDES

Chemotaxis towards carbohydrates is mediated. in enteric bacteria, eit her by the transport-independent, methylation-dependent chemotaxis pat hway or by transport and phosphorylation via the phosphoenolpyruvate ( PEP)-dependent phosphotransferase system (PTS). This study shows that Rhodobacter sphaeroides is chemotactic to a range of carbohydrates but the response involves neither the classical methyl-accepting chemotax is protein (MCP) pathway nor the PTS transport pathway. The chemoattra ctant fructose was transported by a fructose-specific PTS system, but transport through this system did not appear to cause a chemotactic si gnal. Chemotaxis to sugars was inducible and occurred with the inducti on of carbohydrate transport systems and with substrate incorporation. A mutation of the glucose-6-phosphate dehydrogenase gene (zwf) inhibi ted chemotaxis towards substrates metabolized by this pathway although transport was unaffected. Chemotaxis to other, unrelated, chemoattrac tants (e.g. succinate) was unaffected. These data, in conjunction with the fact that mannitol and fructose (which utilize different transpor t pathways) compete in chemotaxis assays, suggest that in R. sphaeroid es the chemotactic signal is likely to be generated by metabolic inter mediates or the activities of the electron-transport chain and not by a cell-surface receptor or the rate or mode of substrate transport.