Regulation of putrescine biosynthesis, critical for phopq signal transduction and magnesium homeostasis in salmonella

The National Institute of Allergy and Infectious Diseases awarded the University of Illinois $186,711 on April 23, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to investigate the regulation of putrescine biosynthesis and its role in PhoQ signal transduction and magnesium homeostasis in Salmonella typhimurium.

The project examines how polyamines and magnesium concentrations are coordinately controlled in bacterial cells and how polyamines substitute for magnesium under low-magnesium stress conditions. The research focuses on understanding mechanisms by which cells regulate polyamine synthesis and export, with particular relevance to Salmonella virulence during macrophage infection. The investigator team plans to characterize how magnesium and polyamine dysregulation affects bacterial physiology and pathogenesis.

Work is performed at the University of Illinois in Urbana, Illinois, with a period of performance from April 23, 2026, through March 31, 2028. This is a Project Grant, which provides funding for innovative research addressing infectious disease challenges. The award supports the recipient's research training and developmental work in infectious diseases and related immunologic areas.

Abstract

Polyamines are organic cations important in all domains of life, but their physiological roles are not well understood. Salmonella typhimurium is a major food-borne pathogen that replicates within macrophages, and adaptation to the low magnesium environment of the macrophage phagosome is key to salmonella virulence. Our recent data support a new paradigm for the overall role of polyamines in cell physiology. Our primary hypothesis is that polyamine and magnesium concentrations are coordinately controlled in the cell and that polyamines replace magnesium in critical systems under low magnesium stress. Upon magnesium starvation, polyamine synthesis is induced, as is production of high affinity magnesium transporters. Either polyamine synthesis or magnesium transport is required to maintain viability. Once magnesium levels are RE-established, the excess polyamines must be excreted, or cells lose viability in stationary phase. This lethality is suppressed by blocking magnesium transport and is exacerbated by increased magnesium in the medium, indicating that IT is the total concentration of magnesium and polyamines that is detrimental. Importantly, these results are recapitulated during infection, confirming that, during infection, magnesium and polyamines are required for the same processes. Although critical for viability and pathogenesis, the mechanisms by which cells coordinately control polyamine and magnesium levels are completely unknown. Our long-term goals are to understand the regulation of polyamine synthesis and export, and the consequences to salmonella physiology when this regulation is disturbed. Our expertise in gene expression and bacterial genetics, combined with the strong phenotypes observed in our salmonella polyamine mutants, put US in a unique position to address these questions. Aim 1: we have shown that the phopq two-component system, the primary regulator of magnesium homeostasis in the cell, is dependent on the polyamine putrescine for function in low magnesium conditions, the normal inducing signal. Specifically, lack of putrescine locks phoq into a state where IT dephosphorylates the transcriptional regulator phop. We will dissect the site and mechanism of putrescine action in phoq. Aim 2: the biosynthetic enzyme spea catalyzes the first step in putrescine synthesis. We have discovered that spea transcription is repressed by putrescine. We will address the mechanisms of this previously unexplored regulation, including identifying the regulatory proteins that are responsible. Completion of the specific aims will provide novel insights into salmonella adaptation to low magnesium, critical for cell viability and virulence of this important pathogen, and likely relevant in all cells.