The Range of Attractant Concentrations for Bacterial Chemotaxis and the Threshold and Size of Response over This Range

Abstract

Attractant was added to a suspension of bacteria (the background concentration of attractant) and then these bacteria were exposed to a yet higher concentration of attractant in a capillary. Chemotaxis was measured by determining how many bacteria accumulated in the capillary. The response range for chemotaxis lies between the threshold concentration and the saturating concentration. The breadth of this range is different for attractants detected by different chemoreceptors. Attractants detected by the same chemoreceptor can have their response ranges in widely different places. Over the center of the response range (on a logarithmic scale), bacteria give similar sized responses to similar fractional increases of concentration, i.e. they respond to ratios of attractant concentration, but the response peaks at the center of the range. The size of the response is different for attractants detected by different chemoreceptors. For a detectable response, a smaller increase in attractant concentration is needed for attractants detected by some chemoreceptors than for attractants detected by others. Although the data are inadequate, it appears that the Weber law may be observed over a wide range of concentrations for some attractants but not for others. In the Appendix we aim to explain some of these results in terms of the interaction of an attractant with its chemoreceptor according to the law of mass action.

Fast, high-throughput measurement of collective behaviour in a bacterial population

“…The chemotactic bias is now a linear function of the relative gradient, shown by the dashed line of best fit (constrained to pass through the origin). This behaviour is interpreted as a change from a low background concentration response regime, where the bacteria respond to absolute changes in concentration to a high-concentration response regime, where they respond to relative change in concentration ('logarithmic sensing'), as previously observed [26]. Semi-empirical mean-field models have been developed [22,27,37] to explain the large dynamic range of the chemotaxis system.…”

Chemotaxis Towards Sugars by Bacillus subtilis

“…The mechanism of bacterial chemotaxis is a subject of wide interest since it is the most primitive sensory-motor process and might be the prototype from which the others have evolved. Increase of attractant concentration brings about increased amounts of attractant-chemoreceptor complex (Adler, 1969 ;Brown & Berg, 1974;Mesibov et al, 1973;Spudich & Koshland, 1975) (considering the chemoreceptor to be binding protein and signaller, see below) which is believed to bind (Ordal & Fields, 1977) to a membrane protein called the methyl-accepting chemotaxis protein (MCP). The MCP is subsequently methylated (Kort et al, 1975;Silverman & Simon, 1977;Springer et al, 1977).…”

Demonstration of a specific neutrophil receptor for a cell-derived chemotactic factor.

“…Current data suggest that chemotactic factors induce cell response by interacting with a receptor (11). If we are indeed measuring a specific receptor responsible for mediating chemotaxis in human neutrophils, a close correlation should exist between the Kd of the receptor and the concentration of the chemotactic factor required to give half-maximal chemotactic response (12,13). The Scatchard analysis of specific 125I-CCF binding revealed the presence of a binding site with a dissociation constant of 0.446 ,uM a value close to the concentration of CCF required to elicit a half-maximal chemotactic response, 1.5 ,uM (5).…”