Molecular Mechanisms of Phosphate Homeostasis in <i>Escherichia coli</i>

Abstract

Life's processes absolutely require inorganic phosphate for structural and energetic purposes. Escherichia coli has developed sophisticated mechanisms to acquire phosphate and to maintain intracellular amounts at optimal levels. The processes by which these simple cells maintain stable intracellular concentrations of phosphate are termed phosphate homeostasis, which involves mechanisms to balance the import, assimilation, sequestration, and export of phosphate. This chapter introduces the proteins involved in phosphate homeostasis and reviews information concerning the multiple phosphate transporters and the mechanisms by which they are regulated. It also introduces new concepts of how this bacterium responds to elevated extracellular levels of phosphate and presents a model for the integration of all of these processes to achieve homeostasis. The predominant importers are PitA, PitB, and the PstSCAB complex. Assimilation, or the incorporation of Pi into organic molecules, occurs primarily through the formation of ATP. Gene regulation relies on the PhoB/PhoR two-component system and the formation of a signaling complex at the membrane. The amount of intracellular phosphate can be fine-tuned through the formation or degradation of polyphosphate. Polyphosphate formation requires adequate supplies of ATP. In addition, when intracellular phosphate levels become too high, phosphate can be exported through PitA, PitB, or the YjbB transporters.

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“…The detection of phosphate regulon response regulator gene (phoB) corroborated well with the phosphate limiting state of the studied AMD samples [14,73,74]. In addition, genes for transport of phosphonate (phnE) and polyphosphate kinase (ppk) further confirmed the abilities of the AMD bacteria in accumulating phosphorous for vital synthesis of macromolecules and support the microorganisms in buffering the cytoplasmic H + ions additionally [75,76].…”

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“…The total phosphorus concentration in E. coli cytosolic FTS was 140 ± 40 mM. The intracellular inorganic phosphate concentration has been reported to be 1–10 mM [ 35 ]. Our concentration was probably higher because the growth media contained a high concentration of phosphate.…”

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“…5E), are of particular interest because inorganic phosphate is an important constituent of energy carrying molecules (e.g., ATP), cofactors (e.g., NADH), and information-storage molecules (e.g., DNA). Therefore, E. coli maintains an optimal homeostatic phosphate level around 1-10 mM [37,38].…”

“…As with charge consumption, proton exchanges between reactants and water is assumed to occur occur on the product side of transport reactions in Eq. (38). Reaction magnesium-consumption is defined in a similar manner…”