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Origin and fate of mutants

Grant number: 21/00610-0
Support type:Regular Research Grants
Duration: August 01, 2021 - July 31, 2023
Field of knowledge:Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
Principal researcher:Beny Spira
Grantee:Beny Spira
Home Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil


Mutations are defined as heritable changes in the DNA sequence of a genome. The frequency with which mutants appear in a population varies according to several factors, among them, the organism species, the locus of the mutation, gain or loss of fitness, presence/expression of DNA repair genes and other elements. In Escherichia coli, PHO-constitutive mutations occur mainly in the pst operon. These mutations cause the loss of function of the PstSCAB phosphate transport system, resulting in the constitutive expression of all PHO regulon genes. This regulon comprises dozens of genes involved in the uptake and assimilation of phosphorus sources in microorganisms. PHO-constitutive mutants are selected in a medium containing glycerol-2-phosphate (G2P) as a carbon source. Wild-type E. coli is unable to take up and metabolize G2P. PHO-constitutive mutants, on the other hand, express high levels of alkaline phosphatase in the periplasm, which in turn hydrolyzes G2P and releases glycerol. Glycerol enters the cell through a system of facilitated diffusion, allowing bacterial growth in the selective medium. It has recently been demonstrated in our laboratory that mutations in the pst operon are quite frequent, but due to the competition of mutants with ancestral wild-type bacteria for the glycerol moieties, only a tiny percentage of PHO-constitutive mutants effectively grow in the selective medium and eventually form colonies. This phenomenon can be characterized as a "tragedy of the commons", in which the vast majority of mutants, and the totality of wild-type bacteria cannot grow. In the present project, we will explore several phenomena related to PHO-constitutive mutants, such as the molecular characterization of these mutants, their fitness, their prevalence in natural E. coli isolates, genetic instability and others. The effect of population density on the frequency of mutants in other mutational systems will also be analyzed. (AU)

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