Vibrio choleraephosphatases required for the utilization of nucleotides and extracellular DNA as phosphate sources

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Abstract

Phosphate is essential for life, being used in many core processes such as signal transduction and synthesis of nucleic acids. The waterborne agent of cholera,Vibrio cholerae, encounters phosphate limitation in both the aquatic environment and human intestinal tract. This bacterium can utilize extracellular DNA (eDNA) as a phosphate source, a phenotype dependent on secreted endo- and exonucleases. However, no transporter of nucleotides has been identified inV. cholerae, suggesting that in order for the organism to utilize the DNA as a phosphate source, it must first separate the phosphate and nucleoside groups before transporting phosphate into the cell. In this study, we investigated the factors required for assimilation of phosphate from eDNA. We identified PhoX, and the previously unknown proteins UshA and CpdB as the major phosphatases that allow phosphate acquisition from eDNA and nucleotides. We demonstrated separable but partially overlapping roles for the three phosphatases and showed that the activity of PhoX and CpdB is induced by phosphate limitation. Thus, this study provides mechanistic insight into howV. choleraecan acquire phosphate from extracellular DNA, which is likely to be an important phosphate source in the environment and during infection.

V. choleraewas previously shown to use extracellular DNA as a source of phosphate. We have identified three phosphatases/nucleotidases that are essential for this phenotype: PhoX, UshA, and CpdB. We also show that UshA is a 5′nucleotidase and that CpdB is a low phosphate activated 3′nucleotidase.

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