Bacteria respond to environmental conditions by regulating genes expression via two main mechanisms: two-component systems and sigma factor competitions. Under stress conditions, such mechanisms are essential bacterial survival and maintenance. In Escherichia coli, the uptake and assimilation of inorganic phosphate (Pi) and organic phosphate compounds is mediated by proteins encoded by the PHO regulon. Some of the genes that belong to the PHO regulon are the pstSCAB-phoU operon, which encodes a high specificity Pi transporter and phoBR, which encodes a two-component system that regulates the transcription of PHO genes. Null mutations in pstSCAB-phoU and some mutations in phoR lead to the constitutive expression of the PHO regulon. Such mutants are called "PHO-constitutive" and are able to grow in medium containing glycerol-2-phosphate as a carbon source. Together with the core RNA polymerase sigma factors form the RNA polymerase holoenzyme. RpoS is a sigma factor that recognizes promoters related to stationary phase and environmental and nutritional stress conditions. In addition, RpoS increases mutation rate. It has been shown that the expression of alkaline phosphatase increases in the absence of RpoS. In the current project, we will investigate the role of RpoS in the emergence of PHO-constitutive mutants. Preliminary results have shown that PHO-constitutive mutants presents different levels of alkalne phosphatase activity. Some mutants are unstable and give off colonies of different phenotypes. Such colonies, here called sergeants, have lost or have attenuated the constitutive expression of phoA, that encodes alkaline phosphatase. We hypothesize that the loss of constitutivity may be related to the cost of expression of the regulon PHO. In this project, we aim to characterize these segregants as well as to gaug the costs of the constitutive expression of the PHO regulon genes.
News published in Agência FAPESP Newsletter about the scholarship: