Bacterial chemotaxis

enteric bacteria are motile: E. coli and Salmonella
importantly, bacteria are so small that they cannot compare concentrations along gradient
therefore must make temporal comparisons
go toward attractants and away from repellents (acids and alcohols)
4-8 flagella

Historical references:
J. Adler, Chemoreceptors in bacteria, Science 166 1588-1597, 1969
TRANSPARENCY Fig 1, Adler, showing attraction to aspartate
like Fig. 15-60, p. 773
J. Adler, The sensing of chemicals by bacteria, Scientific American 234 , #4, April 1976, 40-47

Early, there was question of whether, e.g., galactose metabolism (cf lac operon) was involved
Plenty of evidence that there are actually (multiple) receptors
1. some metabolized molecules do not attract
2a. even if mutations block metabolism, attraction can still be there
2b. chemicals like D-fucose (not used by bacteria) are attractants
3. attraction even if there is still another source of nutrition
4. competion within related compounds but not with others.
5. some mutants block taxis without blocking metabolism
Seemed to be separate receptors for galactose, glucose, ribose, aspartate, serine (5)
Now thinking is that there are 4 (see below)
specific and general mutants which lose chemotaxis
the behavior involves runs and twiddles - vary depending on direction along gradient
TRANSPARENCY Alberts et al., Fig. 15-63, p. 775 - what behavior looks like
counterclockwise - run
clockwise - tumble Text, Fig. 15-62, p. 774 TRANSPARENCY

Newer references:
Alberts et al., pp. 773-778
J.B.Stock, G.S.Lukat & A.M.Stock, Bcterial chemotaxis and the molecular logic of intracellular transduction networks, Ann. Rev. Biophys. Biophys. Chem. 20, 109-136, 1991.
Text, Fig. 15-61, p. 774 TRANSPARENCY - nature of falgellum and motor
flagellin is protein, uses H+ gradient for energy
30 genes to assemble
receptor, Fig. 7, Stock et al., TRANSPARENCY
there are 4 receptors: Tar (for galactose), Tsr, Trg & Tap
How receptors are oriented TRANSPARENCY Fig. 15-65, p. 776
Receptor is methylated at 4 sites for adaptation
TRANSPARENCY Fig. 15-67, p. 777
about 600 amino acids - methylation of glutamates
signalling pathway Stock et al, Fig. 1 and Table 1, TRANSPARENCY
receptors and motors are in membrane but not signalling molecules
Motor switches FliG, FliM and FliN
CheY - 129 amino acids, phosphorylated at Asp57, gets phosphorylated from His48 in CheA
CheY's phosphoaspartyl group is hydrolyzed
CheY is analogous to ras
Chez makes big (20) homopolymer and acts like GAP (GTPase activating protein)
CheA puts phosphate from ATP to histidine
CheAshould have MW of 73,000, but it is 250,000, so multimer
Recall that CheA is soluble, most histidine kinases are membrane
CheA is like src, a tyrosine kinase

This page was last updated on Dec. 19, 2001

Return to Stark home page
Return to Signal Transduction Syllabus