Many bacteria concentrate their chemoreceptors at the cell poles. Chemoreceptor location is important inEscherichia coli, since chemosensory responses are sensitive to receptor proximity. It is not known, however, whether chemotaxis in other bacteria is similarly regulated. To investigate the importance of receptor-receptor interactions in other bacterial species, we synthesized saccharide-bearing multivalent ligands that are designed to cluster relevant chemoreceptors. As has been shown with E. coli, we demonstrate that the behaviors of Bacillus subtilis, Spirochaete aurantia, and Vibrio furnissii are sensitive to the valence of the chemoattractant. Moreover, in B. subtilis, chemotactic responses to serine were increased by pretreatment with saccharidebearing multivalent ligands. This result indicates that, as in E. coli, signaling information is transferred among chemoreceptors in B. subtilis. These results suggest that interreceptor communication may be a general mechanism for modulating chemotactic responses in bacteria.Chemotaxis is a well-studied process that has been explored in diverse bacteria, including Escherichia coli, Salmonella enterica serovar Typhimurium, and Bacillus subtilis (11,14,18,62,76). Chemotaxis is mediated by a series of chemoreceptors that transform chemosensory information into a behavioral response through a two-component system. E. coli serves as the canonical model, and in this species, the two-component signaling system comprises the receptor-associated histidine kinase CheA and the cytoplasmic response regulator CheY (22,65). Changes in chemoreceptor occupancy modulate the kinase activity of CheA, which in turn controls the concentrations of phosphorylated CheY and CheB. Phospho-CheY can interact with the flagellar motor protein FliM (74), thereby influencing the rotation of the flagella and the behavior of the cell (9). The cell is returned to its prestimulatus behavior by the methyltransferase CheR, an enzyme that transfers methyl groups from S-adenosylmethionine to glutamate residues on the cytoplasmic domains of the chemoreceptors (71, 75). Phospho-CheB regulates this adaptation through its methylesterase activity (78). Consequently, the chemoreceptors are termed methyl-accepting chemotaxis proteins (MCPs).Self-association of the MCPs is important for their function. The structures of the MCPs from both E. coli and Salmonella serovar Typhimurium have been investigated by X-ray crystallography and directed cross-linking. The MCPs from both species are stable homodimers (12,19,40,55,56,77). The receptor units are highly helical throughout their periplasmic and cytoplasmic domains. At their cytoplasmic ends, the homodimers associate in a four-helix bundle of two coiled-coils connected by hairpin turns. A recent crystallographic study (40) of the E. coli serine receptor demonstrates that MCPs can oligomerize through the association of their cytoplasmic domains to form a trimer of dimers. In addition, Ames et al. (6) recently provided genetic and biochemical evidence that suggest...

Abstract-Bacterial chemotactic responses are initiated when certain small molecules (i.e., carbohydrates, amino acids) interact with bacterial chemoreceptors. Although bacterial chemotaxis has been the subject of intense investigations, few have explored the influence of attractant structure on signal generation and chemotaxis. Previously, we found that polymers bearing multiple copies of galactose interact with the chemoreceptor Trg via the periplasmic binding protein glucose/galactose binding protein (GGBP). These synthetic multivalent ligands were potent agonists of Escherichia coli chemotaxis. Here, we report on the development of a second generation of multivalent attractants that possess increased chemotactic activities. Strikingly, the new ligands can alter bacterial behavior at concentrations 10-fold lower than those required with the original displays; thus, they are some of the most potent synthetic chemoattractants known. The potency depends on the number of galactose moieties attached to the oligomer backbone and the length of the linker tethering these carbohydrates. Our investigations reveal the plasticity of GGBP; it can bind and mediate responses to several carbohydrates and carbohydrate derivatives. These attributes of GGBP may underlie the ability of bacteria to sense a variety of ligands with relatively few receptors. Our results provide insight into the design and development of compounds that can modulate bacterial chemotaxis and pathogenicity. #