Departments of Microbiology and Plant Pathology and Programs in Biochemistry and Biophysics and Genetics and Cell Biology, Washington State University, Pullman, Washington 99164-4340.
Appl Environ Microbiol. 1987 Apr;53(4):677-82. doi: 10.1128/aem.53.4.677-682.1987.
Plant tissues often contain beta-glucosides that can be enzymatically hydrolyzed to produce toxic aglycones. It has been suggested that the low beta-glucosidase activity found in Erwinia amylovora contributes to bacterial virulence by allowing the bacteria to infect plants that contain beta-glucosides without inducing the formation of toxic aglycones. To test this suggestion, we created strains of E. amylovora which had high beta-glucosidase activities and studied the ability of these strains to cause fire blight disease in pears (Pyrus communis). We isolated spontaneous mutants that were able to utilize beta-glucosides as the sole carbon source and showed that one class had about 10 times as much beta-glucosidase activity as the wild-type strain. In addition, we constructed several plasmids that carry the Escherichia coli bgl operon under the control of a transposon Tn5 promoter that is expressed in E. amylovora. These plasmids were introduced in E. amylovora by transformation. Pathogenesis studies in immature Bartlett pear fruits, etiolated sprouts, and young shoots showed that a 100-fold increase in beta-glucosidase activity does not interfere with normal development of fire blight disease in these model systems.
植物组织通常含有β-葡萄糖苷，可通过酶解产生有毒的配糖体。有人认为，在梨火疫病菌（Erwinia amylovora）中发现的低β-葡萄糖苷酶活性通过允许细菌感染含有β-葡萄糖苷的植物而不诱导有毒配糖体的形成，从而有助于细菌的毒力。为了验证这一假设，我们构建了β-葡萄糖苷酶活性较高的梨火疫病菌株，并研究了这些菌株在梨（Pyrus communis）中引起火疫病的能力。我们分离出能够利用β-葡萄糖苷作为唯一碳源的自发突变体，并发现其中一类的β-葡萄糖苷酶活性比野生型菌株高约 10 倍。此外，我们构建了几个携带大肠杆菌 bgl 操纵子的质粒，该操纵子受转座子 Tn5 启动子的控制，该启动子在梨火疫病菌中表达。这些质粒通过转化引入梨火疫病菌。在不成熟的巴特利特梨果实、黄化芽和嫩枝上的发病机制研究表明，β-葡萄糖苷酶活性增加 100 倍不会干扰这些模型系统中火疫病的正常发展。
