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Growth parameter components of adaptive specificity during experimental evolution of the UVR-inducible mutator Pseudomonas cichorii 302959.

Weigand MR, Tran VN, Sundin GW - PLoS ONE (2011)

Bottom Line: Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times.Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions.These results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.

View Article: PubMed Central - PubMed

Affiliation: Program in Genetics, Michigan State University, East Lansing, Michigan, United States of America.

ABSTRACT

Background: Mutagenic DNA repair (MDR) transiently increases mutation rate through the activation of low-fidelity repair polymerases in response to specific, DNA-damaging environmental stress conditions such as ultraviolet radiation (UVR) exposure. These repair polymerases also confer UVR tolerance, intimately linking mutability and survival in bacteria that colone habitats subject to regular UVR exposure.

Methodology/principal findings: Here, we investigate adaptive specificity in experimental lineages of the highly UVR-mutable epiphytic plant pathogen Pseudomonas cichorii 302959. Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times. Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions.

Conclusions: These results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.

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Related in: MedlinePlus

Relative fitness of ‘fuzzy’ (F) isolates from UVR lineages 25-32.Relative fitness was measured by direct competition with the ancestor under (A) non-UVR and (B) UVR conditions. Single isolates of P. cichorii 302959 exhibiting the ‘fuzzy’ colony morphology were taken after 250 (open bars) and 500 (shaded bars) generations of experimental evolution. Fitness values are means and error bars represent standard error of the mean. Values are significant by two-tailed independent t-test (d.f. = 5, α = 0.05) where indicated (* P<0.05, ** P<0.01, *** P<0.001). P-paired values correspond to two-tailed paired t-tests (d.f. = 5, α = 0.05) between relative fitness values for isolates from generation 250 and 500.
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pone-0015975-g005: Relative fitness of ‘fuzzy’ (F) isolates from UVR lineages 25-32.Relative fitness was measured by direct competition with the ancestor under (A) non-UVR and (B) UVR conditions. Single isolates of P. cichorii 302959 exhibiting the ‘fuzzy’ colony morphology were taken after 250 (open bars) and 500 (shaded bars) generations of experimental evolution. Fitness values are means and error bars represent standard error of the mean. Values are significant by two-tailed independent t-test (d.f. = 5, α = 0.05) where indicated (* P<0.05, ** P<0.01, *** P<0.001). P-paired values correspond to two-tailed paired t-tests (d.f. = 5, α = 0.05) between relative fitness values for isolates from generation 250 and 500.

Mentions: Isolates from UVR lineages expressed two different morphologies, R and F, and single-colony representatives of each from generations 250 and 500 were characterized. Neither morphotype group exhibited a significant fitness advantage under either UVR or non-UVR conditions (all P>0.320). Therefore, measurements of the two groups have been combined when comparing isolates from UVR and non-UVR lineages but are also presented individually to provide additional sampling of the genetic diversity present in UVR lineages. Relative fitness measurements were also conducted using population samples to observe any influence of genotype community structure in UVR lineages. We have combined the relative fitness values determined at generation 250 in this study with previously published measurements at generation 500 [12] in our data analysis and illustrations to highlight differences in adaptive improvements at the two time points. The average relative fitness of all isolates and population samples is summarized in Figure 2 and individual measurements of each lineage are reported in Figures 3, 4, 5, 6. Each relative fitness change was analyzed by an independent t-test against the hypothesis of mean fitness equal to that of the ancestral P. cichorii 302959 (W = 1) and is significant where indicated in the figures. Paired t-tests were also used to determine significant differences in relative fitness between growth environments (UVR vs. non-UVR conditions) or growth intervals (generations 250 vs. 500) and these P values are listed at the bottom of each figure.


Growth parameter components of adaptive specificity during experimental evolution of the UVR-inducible mutator Pseudomonas cichorii 302959.

Weigand MR, Tran VN, Sundin GW - PLoS ONE (2011)

Relative fitness of ‘fuzzy’ (F) isolates from UVR lineages 25-32.Relative fitness was measured by direct competition with the ancestor under (A) non-UVR and (B) UVR conditions. Single isolates of P. cichorii 302959 exhibiting the ‘fuzzy’ colony morphology were taken after 250 (open bars) and 500 (shaded bars) generations of experimental evolution. Fitness values are means and error bars represent standard error of the mean. Values are significant by two-tailed independent t-test (d.f. = 5, α = 0.05) where indicated (* P<0.05, ** P<0.01, *** P<0.001). P-paired values correspond to two-tailed paired t-tests (d.f. = 5, α = 0.05) between relative fitness values for isolates from generation 250 and 500.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3021522&req=5

pone-0015975-g005: Relative fitness of ‘fuzzy’ (F) isolates from UVR lineages 25-32.Relative fitness was measured by direct competition with the ancestor under (A) non-UVR and (B) UVR conditions. Single isolates of P. cichorii 302959 exhibiting the ‘fuzzy’ colony morphology were taken after 250 (open bars) and 500 (shaded bars) generations of experimental evolution. Fitness values are means and error bars represent standard error of the mean. Values are significant by two-tailed independent t-test (d.f. = 5, α = 0.05) where indicated (* P<0.05, ** P<0.01, *** P<0.001). P-paired values correspond to two-tailed paired t-tests (d.f. = 5, α = 0.05) between relative fitness values for isolates from generation 250 and 500.
Mentions: Isolates from UVR lineages expressed two different morphologies, R and F, and single-colony representatives of each from generations 250 and 500 were characterized. Neither morphotype group exhibited a significant fitness advantage under either UVR or non-UVR conditions (all P>0.320). Therefore, measurements of the two groups have been combined when comparing isolates from UVR and non-UVR lineages but are also presented individually to provide additional sampling of the genetic diversity present in UVR lineages. Relative fitness measurements were also conducted using population samples to observe any influence of genotype community structure in UVR lineages. We have combined the relative fitness values determined at generation 250 in this study with previously published measurements at generation 500 [12] in our data analysis and illustrations to highlight differences in adaptive improvements at the two time points. The average relative fitness of all isolates and population samples is summarized in Figure 2 and individual measurements of each lineage are reported in Figures 3, 4, 5, 6. Each relative fitness change was analyzed by an independent t-test against the hypothesis of mean fitness equal to that of the ancestral P. cichorii 302959 (W = 1) and is significant where indicated in the figures. Paired t-tests were also used to determine significant differences in relative fitness between growth environments (UVR vs. non-UVR conditions) or growth intervals (generations 250 vs. 500) and these P values are listed at the bottom of each figure.

Bottom Line: Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times.Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions.These results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.

View Article: PubMed Central - PubMed

Affiliation: Program in Genetics, Michigan State University, East Lansing, Michigan, United States of America.

ABSTRACT

Background: Mutagenic DNA repair (MDR) transiently increases mutation rate through the activation of low-fidelity repair polymerases in response to specific, DNA-damaging environmental stress conditions such as ultraviolet radiation (UVR) exposure. These repair polymerases also confer UVR tolerance, intimately linking mutability and survival in bacteria that colone habitats subject to regular UVR exposure.

Methodology/principal findings: Here, we investigate adaptive specificity in experimental lineages of the highly UVR-mutable epiphytic plant pathogen Pseudomonas cichorii 302959. Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times. Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions.

Conclusions: These results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.

Show MeSH
Related in: MedlinePlus