Department of Biology, Purdue University Fort Wayne, Fort Wayne, IN, USA.
Department of Plant Pathology & Ecology, The Connecticut Agricultural Experiment Station, New Haven, CT, USA.
J Appl Microbiol. 2021 Jun;130(6):2018-2028. doi: 10.1111/jam.14925. Epub 2020 Nov 20.
Erwinia amylovora is the causal agent of fire blight, a devastating disease of apples and pears. This study determines whether the E. amylovora guanine-hypoxanthine transporter (EaGhxP) is required for virulence and if it can import the E. amylovora produced toxic analogue 6-thioguanine (6TG) into cells.
Characterization of EaGhxP in guanine transport deficient Escherichia coli reveals that it can transport guanine, hypoxanthine and the toxic analogues 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 of 3·7 µmol l . An E. amylovora ⊿ghxP::Cam 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.
EaGhxP is not required for virulence, but it does import 6TG into E. amylovora cells.
As part of the disease establishment process, E. amylovora synthesizes and exports a toxic guanine derivative 6TG. Our results are counter intuitive and show that EaGhxP, an influx transporter, can move 6TG into cells raising questions regarding the role of 6TG in disease establishment.
果胶杆菌是火疫病的病原体，火疫病是苹果和梨的毁灭性疾病。本研究旨在确定果胶杆菌鸟嘌呤-次黄嘌呤转运蛋白（EaGhxP）是否是毒力所必需的，以及它是否可以将果胶杆菌产生的有毒类似物 6-硫代鸟嘌呤（6TG）导入细胞。
在缺乏鸟嘌呤转运的大肠杆菌中对 EaGhxP 的特性进行了表征，结果表明它可以转运鸟嘌呤、次黄嘌呤以及有毒类似物 8-氮杂鸟嘌呤（8AG）和 6TG。同样，EaGhxP 也可以将 8AG 和 6TG 转运到果胶杆菌细胞中。EaGhxP 对 6TG 的亲和力很高，K 值为 3.7 μmol l。果胶杆菌 ΔghxP::Cam 菌株对 8AG 和 6TG 的生长表现出抗性。尽管 EaGhxP 在活性疾病传播期间表达，但在不成熟的苹果和梨试验中，它对毒力并非必需。
EaGhxP 不是毒力所必需的，但它确实可以将 6TG 导入果胶杆菌细胞。
作为疾病建立过程的一部分，果胶杆菌合成并输出一种有毒的鸟嘌呤衍生物 6TG。我们的结果与直觉相悖，表明作为内流转运蛋白的 EaGhxP 可以将 6TG 转运到细胞中，这引发了关于 6TG 在疾病建立中的作用的问题。
