Table 1

The stresses tested, and their influence on average relative mutation effects
Stress
 Strength
 ε
 *
Lethal†
 Bias‡
 p§
Acidic stress
 pH 5
 0.19
 0.27
 0.30
 0.11
 -0.18
 < 0.01
Unsupplemented¥
 30% old supernatant
 0.31
 0.27
 0.26
 0
 0.02
 NS
High osmolarity
 600 mM NaCl
 0.43
 0.28
 0.25
 0.05
 0.05
 NS
Dithiothreitol
 1.6 mg/ml
 0.30
 0.29
 0.21
 0.05
 0.26
 < 0.01
Trimethoprim
 0.4 μg/ml
 0.53
 0.28
 0.10
 0.05
 0.33
 < 0.0001
Chloramphenicol
 1 μg/ml
 0.43
 0.28
 0.15
 0
 0.30
 < 0.001
Low temperature
 17°C
 1.77
 0.27
 0.15
 0.05
 0.07
 < 0.03

η = log(νF / νS) representing the reduction of the parental strain's growth rate by the stress. The average relative mutation effects and are defined in Figure 1 and are calculated here as median values of the mutant library. *Measurements of mutant growth rates in the favorable environment were repeated in parallel with each of the stress measurements. †'Lethal' indicates the fraction of mutants showing growth in the favorable media but no growth under stress after one week. ‡Bias ≡ (-)/ε represents a bias towards alleviation of the mutations' effects under the stress. §The p value is from a paired Student's t-test for the difference between mutation effects under stress and under favorable conditions; NS, not significant (p > 0.05). Acid stress is 0.25 mM sorbic acid and 16 mM citric acid. ¥The standard favorable environment is defined as 'unsupplemented' stress and is compared to an even more favorable environment constructed by supplementing it with 30% supernatant of an old culture (see text for further details).

Kishony and Leibler Journal of Biology 2003 2:14   doi:10.1186/1475-4924-2-14