Background

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Background
E. coli in Motion, Chapter 2
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Pfeffer assay Congregation of bacteria at mouth
of capillary containing meat extract
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?
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Chemoreceptors in bacteria Julius Adler
1. What are the bacteria attracted to? 2. What
is the mechanism of attraction?
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Method
E. coli in Motion, Chapter 3
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A quantitative method for studying chemotaxis
Attraction of bacteria to aspartate
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Galactose Ribose Aspartate Serine
Chemotaxis towards glucose but not toward glycerol
Metabolized chemicals are not necessarily
attractants
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Readily metabolized chemicals are not necessarily
attractants
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Is the response to the attractant itself, or its
metabolic product or the energy produced?
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First products of metabolism do not attract
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Mutants that cannot metabolize a chemical are
still attracted to it
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Non-metabolizable analogs attract
Non-metabolizable glucose analogs such as 2-deoxy
glucose also attract
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Metabolized chemicals do not block
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1. Metabolic products are not attractants 2.
Non-metabolized chemicals are attractants 3.
Metabolized chemicals do not block attractants
What determines the specificity of this response?
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Structurally related compounds compete
Fucose/galactose galactose
Aspartate/serine serine
Idea of specific receptors
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Mutants that cannot metabolize a chemical are
still attracted to it
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Mutants that fail to do chemotaxis but can still
metabolize also argues for specific receptors
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How many receptors?
GBP-Trg
GBPTrg
PTS??
RBP -Trg
Tar
Tsr
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Mutants that fail to transport can still do
chemotaxis
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Chemoreceptors in bacteria Julius Adler
1. What are the bacteria attracted to? 2. What
is the mechanism of attraction?
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1. What are the bacteria attracted to?
SUMMARY To serve as
attractants 1. Metabolism is not necessary. 2.
Transport is not necessary. 3. Structure
important for recognition by receptors
(Different classes of receptors)
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2. What is the mechanism of attraction?
HYPOTHESES/SPECULATION
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Knowlegde increases not by the direct perception
of truth, but by the relentless bias toward
perception of error.
Kenneth
Boulding
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Why are only a subset of amino acids and sugars
attractants?
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Plate assay for chemotaxis
Che-
Wild-type