Directed mutation: between unicorns and goats

Foster, Patricia L.

doi:10.1128/jb.174.6.1711-1716.1992

Cited by 64 publications

(37 citation statements)

References 42 publications

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“…But it is interesting that the original Roth-Stahl hypothesis has VOL. 186, 2004 DIALOG 4849 evolved so that it is now almost exactly what Cairns and I proposed years ago (18,20,23).…”

Section: Amplificationmentioning

confidence: 87%

Adaptive Mutation in Escherichia coli

Foster¹

2000

Cold Spring Harbor Symposia on Quantitative Biology

102

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In 1988 John Cairns, Julie Overbaugh, and Stephan Miller published a paper entitled "The origin of mutants," in which they suggested that bacteria could choose which mutations to make (11). Shortly thereafter, Cairns and I began collaborating on a National Science Foundation-funded project to investigate the genetic basis of what was popularly called "directed mutation" (although at the time we were calling it "selectiondependent mutation," which now seems as good a name as any). Our plan was to mutagenize an appropriate strain of Escherichia coli and identify and characterize variants defective in selection-dependent mutation. Cairns and coworkers had been investigating a strain called SM195, described in their original paper (11). However, the mechanisms of mutation in this strain had proved to be complicated, and we wanted a new experimental subject. We were setting up to investigate selection-induced activation of the cryptic bgl operon (36), when Jeffrey Miller gave us a Lac Ϫ strain, called ␣45, that he said had a high rate of reversion to Lac ϩ after plating on minimum lactose medium. The lac allele in this strain is a fusion of lacI to lacZ that eliminates the lac regulatory region as well as several residues of lacI and lacZ; transcription of the fusion is constitutive, initiating at the lacI promoter (7). ␣45 has a ϩ1 frameshift mutation, lacI33, in the lacI coding region (12). Miller and coworkers have used several similar strains to study various mutational mechanisms (52, 67). As in many of the strains that originated with Jacob and Monod, proAB and lac are deleted from the chromosome and carried on an episome, FЈ128. This arrangement greatly facilitates genetic manipulations and turned out to be important to adaptive mutation. We mated the episome from ␣45 into a ⌬(lac-pro) recipient that we had made rifampin resistant and named the new strain FC40 (Foster and Cairns #40).In our first paper (10), we showed that Lac ϩ revertants of FC40 accumulate at a constant rate for about a week after the cells are plated on minimal lactose plates. Two days after plating (the first day that Lac ϩ colonies appear), the numbers of mutants among cultures has a Luria-Delbrück distribution (meaning that the mutations occurred prior to plating), whereas on subsequent days the distribution becomes Poisson (meaning that the mutations occurred after plating). After 5 days on lactose plates, there are about 100 Lac ϩ colonies per 10 8 cells plated. We calculated that the normal preplating mutation rate was about 10 Ϫ9 Lac ϩ revertants per cell per generation, whereas the postplating mutation rate was about 10 Ϫ9 per cell per h; considering that the doubling time in minimal medium is about an hour, this means that per unit time, the two mutation rates are the same. We have never figured out if this similarity is informative or merely a coincidence.The high postplating reversion rate of FC40 allowed us to eliminate a number of artifactual explanations for the phenomenon. In our first paper (10) we ruled out the possibility ...

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“…But it is interesting that the original Roth-Stahl hypothesis has VOL. 186, 2004 DIALOG 4849 evolved so that it is now almost exactly what Cairns and I proposed years ago (18,20,23).…”

Section: Amplificationmentioning

confidence: 87%

Adaptive Mutation in Escherichia coli

Foster¹

2000

Cold Spring Harbor Symposia on Quantitative Biology

102

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“…Mutational events are the product of all mutagenic and antimutagenic forces (Smith, 1992) but starvation is not, of itself, believed to be mutagenic (Foster, 1992). Although starvation can trigger transposition it is unlikely that such events are directly involved in the mutations described here.…”

Section: Possible Mechanisms For the Emergence Of Mutationsmentioning

confidence: 90%

Mutations to antibiotic resistance occur during the stationary phase in Lactobacillus plantarum ATCC 8014

Thompson¹,

McConville²,

McReynolds³

et al. 1997

Microbiology

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When Lactobacillus planfarum ATCC 8014 was maintained in LCM broth (which consists of buffered tryptone and is sufficient to support the growth of some species of Lactobacillus) for long periods (1120 d), viable bacteria persisted. Rifampicin-, streptomycin-and sodium-fusidate-resistant mutants were recovered from parallel LCM broth cultures following a stochastic pattern. Individual cultures appeared to yield mutants intermittently. One culture in particular yielded rifampicin-resistant colonies at a frequency of 1 in I00 viable bacteria after 20 d incubation and these persisted until the experiment was terminated a t 115 d. In a separate experiment two parallel cultures yielded mutants resistant to low concentrations of streptomycin a t a similar frequency. Using a chemostat it was shown that in continuous culture in LCM at slow growth rates the highest frequency of recovery of antibiotic-resistant mutants was achieved when the bacteria exhibited doubling times of 90 h or greater. The frequency of recovery of mutants was as high as 1 in 1000 viable bacteria. Thus, mutations to antibiotic resistance in L. plantarum ATCC 8014 can take place in the absence of measurable cell division. The data are consistent with the notion that populations of starved bacteria in stationary phase can be genetically dynamic.

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“…Moreover, these mutations only occur in genes whose products or functions are relevant to the selecting environment. Adaptive changes may occur in both bacteria (Escherichia colz) and yeast (J. cereviside), although reports continue to generate controversy (Foster, 1992;Mittler & Lenski, 1992;Stahl, 1992). To absolutely eliminate the possibility of all growth or cell turnover in a limiting but non-lethal environment is difficult and thus exposes many claims of adaptive mutagenesis to criticism (Mittler & Lenski, 1992).…”

Section: Discussionmentioning

confidence: 99%

Isolation of a conditional suppressor of leucine auxotrophy in Saccharomyces cerevisiae

Heinemann

Ankenbauer²,

Horecka³

1994

Microbiology

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OR 97403, USAPhenotypically and genotypically (/eu2-3,112) Leu-cells of Saccharomyces cerevisiae gave rise to small colonies on medium devoid of leucine. This only occurred on plates with a high density of Leu-cells or on medium supplemented with limiting quantities of leucine. Cells from these small colonies retained a growth advantage over their parent on limiting leucine supplements even after growth in a non-selecting (rich) medium. Therefore, the growth variants had acquired a heritable change. The phenotype was recessive and due to a change in a nuclear gene unlinked to the LEU2 locus. The phenotype provided a growth advantage only during leucine starvation; growth of the variants was indistinguishable from their parent on medium lacking the other essential supplements (histidine and uracil) required for the growth of the strain.[14C]Leucine uptake assays demonstrated that the variants were better able than their parents to accumulate leucine from their environments, and this ability extended to other hydrophobic amino acids. These results suggest that in the variants an amino acid uptake system has been derepressed rather than there having been reversion or extragenic suppression of the mutation in leucine biosynthesis. We designate the mutant gene responsible for the phenotype /up1 (for leucine uptake). The transport characteristics of the /up1 mutants suggested that LUPl is a regulatory component of an ammonium-regulated hydrophobic amino acid uptake system.

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Directed mutation: between unicorns and goats

Cited by 64 publications

References 42 publications

Adaptive Mutation in Escherichia coli

Adaptive Mutation in Escherichia coli

Mutations to antibiotic resistance occur during the stationary phase in Lactobacillus plantarum ATCC 8014

Isolation of a conditional suppressor of leucine auxotrophy in Saccharomyces cerevisiae

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