Abstract
One of the most important achievements of bacteria is its capability to adapt to the changing conditions of the environment. The competition for nutrients with other microorganisms, especially in the soil, where nutritional conditions are more variable, has led bacteria to evolve a plethora of mechanisms to rapidly fine-tune the requirements of the cell. One of the essential nutrients that are normally found in low concentrations in nature is inorganic phosphate (Pi). Bacteria, as well as other organisms, have developed several systems to cope for the scarcity of this nutrient. To date, the unique mechanism responding to Pi starvation known in detail is the Pho regulon, which is normally controlled by a two component system and constitutes one of the most sensible and efficient regulatory mechanisms in bacteria. Many new members of the Pho regulon have emerged in the last years in several bacteria; however, there are still many unknown questions regarding the activation and function of the whole system. This review describes the most important findings of the last three decades in relation to Pi regulation in bacteria, including: the PHO box, the Pi signaling pathway and the Pi starvation response. The role of the Pho regulon in nutritional regulation cross-talk, secondary metabolite production, and pathogenesis is discussed in detail.
Highlights
Phosphorus, in terms of cellular content, is the fifth most important element
Inorganic phosphate depletion in the medium has been shown to be essential for activation of the Pho regulon in bacteria; differing with other microorganisms such as Saccharomyces cerevisiae, in which the intracellular Pi concentration seems to account for this activation (Auesukaree et al, 2004)
The physiological response to Pi-starvation in bacteria is a good example for systems biology studies, because it constitutes a fast and very sensible responding system, and because it generates an amazing regulatory network with few precedents in bacteria, involving primary and secondary metabolisms, virulent factors, and multiple cross-talks in some cases
Summary
Phosphorus, in terms of cellular content, is the fifth most important element. It is essential for several important biological processes such as the inheritance of genetic materials, energy metabolism, membrane integrity, and intracellular signaling. The availability of this nutrient has many medical, agricultural, and pharmaceutical implications. Phosphorus is required to ensure high levels of agricultural productivity (Ha and Tran, 2014). With this aim, modern agricultural practice extensively uses fertilizers, in many cases producing negative environmental effects. Companies are often forced to use low concentrations of this nutrient which results in a significant decrease of the growth yields
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