The guanine–hypoxanthine permease GhxP of Erwinia amylovora facilitates the influx of the toxic guanine derivative 6‐thioguanine

Abstract

Aim Erwinia amylovora is the causal agent of fire blight, a devastating disease of apples and pears. This study determines if the Erwinia amylovora guanine‐hypoxanthine transporter (EaGhxP) is required for virulence and if it can import the E. amylovora produced toxic analog 6‐thioguanine (6TG) into cells. Methods and Results Characterization of EaGhxP in guanine transport deficient Escherichia coli reveals it can transport guanine, hypoxanthine and the toxic analogs 8‐azaguanine (8AG) and 6TG. Similarly, EaGhxP transports 8AG and 6TG into E. amylovora cells. EaGhxP has a high affinity for 6TG with a K_i of 3.7 µmol l^‐1. An E. amylovora ΔghxP::Cam^r strain shows resistance to growth on 8AG and 6TG. Although EaGhxP is expressed during active disease propagation, it is not necessary for virulence as determined on immature apple and pear assays. Conclusions EaGhxP is not required for virulence, but it does import 6TG into E. amylovora cells.