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Chemotactic response of soil
bacteria to leaf decay products.
A. Plus Student
Biology 5, Section 90/91
ncbb:2000
What did we want to find out?
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Experiment One: Does Cellulomonas
respond differently to sugars from
cellulose and hemicellulose?
Experiment Two: Can we predict how
Cellulomonas will respond to cellobiose?
How we measured “response”
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Both experiments used the same
chemotaxis assay procedure.
Plate, then count
Buffer
Only
Buffer +
Attractant
Calculate
Relative
Response
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Results: Experiment One
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Group
N
Mean
SD
Cellobiose
Hemicellulose
15
15
13.5
5.4
2.16
1.72
Mean relative response was greater for
cellobiose than for hemicellulose sugars.
T-test probability < 0.0001
Rejected Ho; Accepted Ha
Results: Experiment One
Relative response
(kilocells)
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Cellobiose
Hemicellulose products
Chemical tested
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Mean relative response values were
significantly different.
Results: Experiment Two
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Cellulomonas response to cellobiose
increased as sugar concentration
increased.
MODEL:
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Rel. Resp. = 8.412 + 3.242*Cellobiose conc.
Test of Fit probability < 0.0001
Rejected Ho; Accepted Ha
Results: Experiment Two
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The model does a good job of predicting
relative response as a function of sugar
concentration.
Our answers are…
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Experiment One: Does Cellulomonas
respond differently to sugars from
cellulose and hemicellulose?
YES
Experiment Two: Can we predict how
Cellulomonas will respond to cellobiose?
YES
Biological answers…
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Cellulomonas shows a strong response to
an abundant food source.
The number of Cellulomonas attracted
to a food source depends on the
concentration of the source chemical.
…and their meaning.
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More surface receptor-proteins specific
to cellobiose than to sugars from
hemicellulose.
Cellulomonas is well-adapted for its
ecological role.
Decomposition
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