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  • 1
    In: BMC Biology, Springer Science and Business Media LLC, Vol. 18, No. 1 ( 2020-12)
    Abstract: It is widely assumed that all mutant microorganisms present in a culture are able to grow and form colonies, provided that they express the features required for selection. Unlike wild-type Escherichia coli , PHO-constitutive mutants overexpress alkaline phosphatase and hence can hydrolyze glycerol-2-phosphate (G2P) to glycerol and form colonies on plates having G2P as the sole carbon source. These mutations mostly occur in the pst operon. However, the frequency of PHO-constitutive colonies on the G2P selective plate is exceptionally low. Results We show that the rate in which spontaneous PHO-constitutive mutations emerge is about 8.0 × 10 −6 /generation, a relatively high rate, but the growth of most existing mutants is inhibited by their neighboring wild-type cells. This inhibition is elicited only by non-mutant viable bacteria that can take up and metabolize glycerol formed by the mutants. Evidence indicates that the few mutants that do form colonies derive from microclusters of mutants on the selective plate. A mathematical model that describes the fate of the wild-type and mutant populations under these circumstances supports these results. Conclusion This scenario in which neither the wild-type nor the majority of the mutants are able to grow resembles an unavoidable “tragedy of the commons” case which results in the collapse of the majority of the population. Cooperation between rare adjacent mutants enables them to overcome the competition and eventually form mutant colonies. The inhibition of PHO-constitutive mutants provides an example of mutant frequency masked by orders of magnitude due to a competition between mutants and their ancestral wild-type cells. Similar “tragedy of the commons-like” cases may occur in other settings and should be taken into consideration while estimating true mutant frequencies and mutation rates.
    Type of Medium: Online Resource
    ISSN: 1741-7007
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2020
    detail.hit.zdb_id: 2133020-7
    SSG: 12
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  • 2
    In: Nucleic Acids Research, Oxford University Press (OUP), Vol. 48, No. 22 ( 2020-12-16), p. 12804-12816
    Abstract: HK022 coliphage site-specific recombinase Integrase (Int) can catalyze integrative site-specific recombination and recombinase-mediated cassette exchange (RMCE) reactions in mammalian cell cultures. Owing to the promiscuity of the 7 bp overlap sequence in its att sites, active ‘attB’ sites flanking human deleterious mutations were previously identified that may serve as substrates for RMCE reactions for future potential gene therapy. However, the wild type Int proved inefficient in catalyzing such RMCE reactions. To address this low efficiency, variants of Int were constructed and examined by integrative site-specific recombination and RMCE assays in human cells using native ‘attB’ sites. As a proof of concept, various Int derivatives have demonstrated successful RMCE reactions using a pair of native ‘attB’ sites that were inserted as a substrate into the human genome. Moreover, successful RMCE reactions were demonstrated in native locations of the human CTNS and DMD genes whose mutations are responsible for Cystinosis and Duchene Muscular Dystrophy diseases, respectively. This work provides a steppingstone for potential downstream therapeutic applications.
    Type of Medium: Online Resource
    ISSN: 0305-1048 , 1362-4962
    RVK:
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2020
    detail.hit.zdb_id: 1472175-2
    SSG: 12
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