The Gram-negative enterobacterium Erwinia amylovora causes fire blight disease in apple and pear trees. Lipopolysaccharides and the exopolysaccharide amylovoran are essential E. amylovora virulence factors. We found that mutations in rfbX disrupted amylovoran production and virulence in apple fruits and tree shoots and that the deletion of yibD suppressed the rfbX mutant phenotype. The level of expression of yibD was about 10-fold higher in the ΔrfbX mutant than the wild type. A forward genetic suppressor screen in the ΔrfbX mutant uncovered multiple mutations in yibD and supported the conclusion that the virulence defect of rfbX mutants is due to reduced amylovoran production. The yibD and rfbX genes are expressed as a two-gene operon, yibD rfbX. The rfbX gene encodes a previously uncharacterized putative polysaccharide subunit transporter, while yibD encodes a predicted glycosyltransferase. Mutation of rfbX did not have a detectable effect on lipopolysaccharide patterns; however, the overexpression of yibD in both the wild-type and ΔyibD ΔrfbX genetic backgrounds disrupted both amylovoran and lipopolysaccharide production. Additionally, the overexpression of yibD in the ΔyibD ΔrfbX mutant inhibited bacterial growth in amylovoran-inducing medium. This growth inhibition phenotype was used in a forward genetic suppressor screen and reverse-genetics tests to identify several genes involved in lipopolysaccharide production, which, when mutated, restored the ability of the ΔyibD ΔrfbX mutant overexpressing yibD to grow in amylovoran-inducing medium. Remarkably, all the lipopolysaccharide gene mutants tested were defective in lipopolysaccharide and amylovoran production. These results reveal a genetic connection between amylovoran and lipopolysaccharide production in E. amylovora.

中文翻译：

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淀粉欧文氏菌推定多糖转运蛋白家族成员的毒力遗传学。

革兰氏阴性肠杆菌欧文氏小球藻在苹果树和梨树中引起火疫病。脂多糖和胞外多糖amylovoran是必不可少的解淀粉链球菌毒力因子。我们发现，在突变rfbX打乱amylovoran生产和毒力在苹果的水果和树芽和删除的yibD抑制rfbX突变表型。的表达水平的yibD是在Δ大约高10倍rfbX突变体比野生型。在Δ的正向遗传抑制器屏幕rfbX在突变体未覆盖的多个突变的yibD并支持以下结论：rfbX突变体的毒力缺陷是由于戊基戊酸产量降低所致。该的yibD和rfbX基因被表达为双基因操纵子的yibD rfbX。所述rfbX基因编码一种以前未推定的多糖亚基转运，而的yibD编码糖基转移酶的预测。rfbX的突变对脂多糖模式没有可检测的影响。然而，过量表达的yibD在野生型和Δ两者的yibD Δ rfbX遗传背景破坏了阿伏龙和脂多糖的生产。此外，过表达的yibD在Δ的yibD Δ rfbX突变体amylovoran诱导培养基抑制细菌生长。这种生长抑制表型在向前的遗传抑制屏幕使用和反向遗传学测试，以鉴定参与脂多糖生产，这突变时，恢复了Δ的能力的几个基因的yibD Δ rfbX突变体过度表达的yibD在诱导戊基戊酸的培养基中生长。值得注意的是，所有测试的脂多糖基因突变体在脂多糖和戊酰戊聚糖生产方面均存在缺陷。这些结果表明在amylovoran和脂多糖生产之间的遗传连接E.火疫病菌。