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Nucleobase transport in Erwinia amylovora

Neil Schultes: The Connecticut Agricultural Experiment Station

<div><em>Erwinia amylovora</em>, a phytopathogenic bacterium, causes fire blight of apples and pears. It derives nutrients from the host during disease progression. Our research 1) identifies <em>E. amylovora</em> nucleobase transporter loci, 2) biochemically characterizes the encoded transporters and 3) determines if the loci are necessary for disease. Previous work revealed that <em>E. amylovora</em> nucleobase biosynthetic mutants differ in their ability to cause disease, suggesting either varied uptake or importance of nucleobases. Here the transport function and biochemical properties for four nucleobase cation symporter 2 transporters in <em>E. amylovora</em> are determined through heterologous expression in nucleobase transport deficient <em>Escherichia coli </em>Keio strains coupled with radiolabeled nucleobase uptake studies and toxic analog growth studies. Under <em>in vitro </em>culture conditions, the uracil transporter, EaUraA, is able to transport uracil and 5-fluorouracil into <em>E. coli </em>cells. Similarly, the guanine/hypoxanthine transporter, EaG/HXP, moves guanine, hypoxanthine, 8-azaguanine and 6-thioguanine; the adenine transporter, EaAdeP, transports adenine, guanine and 8-azaadenine; and the xanthine transporter, EaXanP, moves xanthine. Finally, mutations of the <em>uraA</em> or <em>ghxP</em> or <em>adeP </em>loci in <em>E. amylovora</em> do not impair pathogenicity. Our results confirm that nucleobase transporter genes are present and functional in <em>E. amylovora </em>yet they are not required for disease progression.</div>