Bacterial cells experience stress when they accumulate sugar-phosphates, and the ways in which bacteria deal with this stress have only recently begun to be characterized. Certain enteric bacteria like Escherichia coli possess a mechanism to alleviate glucose-phosphate stress, a condition in which growth is hindered due to the accumulation of glucose-phosphate in the cell. The transcriptional regulator SgrR and the regulatory small RNA SgrS mediate the glucose-phosphate stress response. SgrR activates transcription of sgrS, and in turn SgrS helps to restore growth through translation inhibition and subsequent degradation of the mRNA ptsG, encoding the major glucose transporter EIICBGlc. sgrR and sgrS mutants each exhibit growth defects when grown under glucose-phosphate stress. Although this facet of the stress response is well-described, little is known about how it affects other aspects of cell physiology, and determining this is an overall goal of the proposed research. For example, preliminary data suggests a role for PitA, a transporter of inorganic phosphate, in the glucose-phosphate stress response: pitA expression is decreased during stress, and mutations in pitA partially rescue the growth defect of an sgrS mutant. This project has two objectives, both of which involve examining additional features of the glucose-phosphate stress response: 1) characterize the role of PitA during stress, and 2) identify novel regulatory targets of SgrR. First, we propose that deletion of pitA alleviates stress by either inducing particular genes in the phosphate (Pho) regulon (which is induced under phosphate starvation conditions) and/or decreasing transport through EIICBGlc (which requires phosphorylation to be activated). To test these hypotheses, we first will confirm that pitA is repressed during glucose-phosphate stress. We next will see if particular Pho genes cause the stress relief by deleting individual Pho genes in an sgrS pitA mutant to determine if the growth rescue is lost. In addition, we will establish whether uptake of phosphate is limited during glucose-phosphate stress, and whether limitation of phosphate affects induction of the stress response and/or decreases transport through EIICBGlc. We will also determine whether decreased phosphate levels alleviate the glucose-phosphate growth defects of sgrR and sgrS mutants. Second, to uncover other as-yet-unrecognized aspects of the glucose-phosphate stress response, we will use microarray analyses to identify additional genes regulated by SgrR, and test the ability of SgrR to bind to target gene promoters. We will next examine the roles of individual SgrR regulon members by testing regulon gene mutants for the ability to recover from glucose-phosphate stress. Studying the response to glucose-phosphate stress could aid not only in our general understanding of how bacteria regulate their cellular physiology in response to environmental stresses, but also could uncover new cellular targets that stress bacteria and could be used to foil bacterial pathogens.
This research proposes to study how a bacterium that causes disease responds to a particular stress in its environment. This stress involves the bacterium taking up too much sugar, which is toxic to it. By studying how the bacterium deals with this stress, we will learn about how sugars can be toxic to cells (as they are in people with diabetes), as well as possibly identify new ways to stress harmful bacteria and prevent them from causing disease.
|Richards, Gregory R; Patel, Maulik V; Lloyd, Chelsea R et al. (2013) Depletion of glycolytic intermediates plays a key role in glucose-phosphate stress in Escherichia coli. J Bacteriol 195:4816-25|
|Richards, Gregory R; Vanderpool, Carin K (2012) Induction of the Pho regulon suppresses the growth defect of an Escherichia coli sgrS mutant, connecting phosphate metabolism to the glucose-phosphate stress response. J Bacteriol 194:2520-30|