The study compares the phenomenon observed in E. coli to the “tragedy of the commons”, in which individual interests take precedence over the collective good. It hides the emergence of variants and makes the colony mutation rate appear lower.
A study by researchers at the University of Sao Paulo, Brazil, showed that competition for nutrients, lack of cooperation between Escherichia coli bacteria in the same population, and in cases of food scarcity, prevented mutations that better adapt to the environment from flourishing. Except for those organized in small groups. This phenomenon masks the emergence of new bacterial variants, making the mutation rate appear to be lower than it actually is.
Mutants appear constantly and accumulate from generation to generation. The mutation frequency determines the development of a particular species. Understanding the origin of mutations is also important to explain biological processes. In the case of bacteria, for example, this helps explain the possible evolutionary difference of a pathogen in an epidemic or antibiotic resistance.
In an article about the study published in the journal BMC BiologyResearchers compare what happens in the Escherichia coli colonies to the “tragedy of the commons,” a term used by economists and environmental scientists to refer to the problems that occur when individuals pursue personal gain at the expense of their community, resulting in the destruction of public goods or natural resources.
“In times of nutritional scarcity, bacteria do not interact for mutual benefit, to ensure colony growth. We have found that even the emergence of a small number of individuals who can use the available food sources does not prevent this lack of cooperation from endangering the entire population,” said Benny Spira, professor at University Institute of Biomedical Sciences (ICB-USP) and the latest author of the article, “Only a few mutants are able to reproduce and form new colonies.”
This discovery explains the long-standing question of why the frequency of mutations capable of splitting certain nutrients (breaking them down into molecules that can be metabolized) is always much less in practice than in theory.
Research on mutant frequency cloaking is part of a project supported by the São Paulo Research Foundation – FAPESP through a regular research grant, PhD grant, and scientific initiation grant.
Tragedy of the whole
Unlike wild type E. coli, bacteria with mutagenic PHO overexpress the enzyme alkaline phosphatase and thus can cleave glycerol-2-phosphate (G2P) to release phosphate and glycerol, which is an important source of carbon, especially in cases of scarcity of nutrition. PHO stands for phosphate. PHO Regulon helps plant cells survive and grow despite scarce nutrients and phosphate depletion in the environment.
The frequency of PHO-forming colonies on G2P selective plates (cell culture dishes) is exceptionally low. “When we measure the actual frequency of the mutations, we find that in a community of 100 billion bacteria there are tens of thousands of mutants that make up PHO. However, only 50 to 100 can reproduce and produce new colonies with the mutation that confers the ability to cleave G2P,” Spira said. .
He explained that the mutant is able to express large amounts of alkaline phosphatase, which is fractionated at the periphery of the cell (the area between the inner cytoplasmic membranes and the outer membranes). Thus when G2P is cleaved and glycerol is produced, the nutrients can be stored by the bacteria or released into the external environment, where they will be taken up immediately by the numerous (non-mutant) wild bacteria in the vicinity.
However, the glycerol released by the mutants is not sufficient for the growth of colonies of wild-type bacteria. About 20,000 bacteria can be found near each mutation. “The few mutations that succeed in reproducing are those that cooperate with each other to form groups and swap glycerol. Otherwise, nutrients become scarce, the mutations are inhibited, and the population dies,” Spira said.
Wild and mutant bacteria usually compete for insufficient glycerol. “The mutants do not reproduce due to the scarcity of this nutrient, which creates the impression that there are no mutations and significantly reduces the frequency of PHO-forming mutations in the population,” he said.
Therefore, inhibition of PHO-forming mutants is an example of mutation frequency induced by competition between mutants and their wild-type ancestral cells. “The example shows that situations similar to the” tragedy of the commons “may occur in other places and must be taken into account when estimating the mutation rates, he said.
About the Sao Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution whose mission is to support scientific research in all areas of knowledge by granting scholarships, fellowships, and grants to researchers associated with higher education and research institutions in the state of São Paulo, Brazil. FAPESP understands that the best research can only be done by working with the world’s best researchers. Therefore, it has established partnerships with funding agencies and higher education, private companies and research organizations in other countries known for the quality of its research and encourages the scholars funded by its grants to further develop their international cooperation. You can learn more about FAPESP at http: // www.