The type IV fimbrial subunit gene (fimA) of Dichelobacter nodosus is essential for virulence, protease secretion, and natural competence
The type IV fimbrial subunit gene (fimA) of Dichelobacter nodosus is essential for virulence, protease secretion, and natural competence
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DOI：
10.1128/jb.183.15.4451-4458.2001
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发表时间：
2001-08-01
影响因子：
3.2
通讯作者：
Rood, JI
中科院分区：
文献类型：
--
作者：
Kennan, RM;Dhungyel, OP;Rood, JI
结节双歧杆菌是引起绵羊蹄疾的重要病原。与该病有关的主要致病因子是IV型菌毛和胞外蛋白水解酶。为了研究菌毛在致病力中的作用，采用等位基因交换的方法对编码菌毛亚单位蛋白的FIMA基因进行了插入失活。结瘤菌株VCS1703A。对两个独立产生的FIMA突变体的详细分析表明，它们不再产生菌毛亚单位蛋白或完整的菌毛，也不表现出抽动运动。此外，这些突变体不再能够进行自然转化，也不能分泌野生型的胞外蛋白酶。这些效应不是由于下游FIMB基因的极性效应造成的，因为插入失活的FIMB突变体在这些表型测试中都没有缺陷。在受控环境条件下进行的羊圈试验中，对突变体的毒力测试表明，FimA突变体是无毒的，这为FimA基因是结节扇贝的必需毒力基因提供了证据。这些研究代表了分子遗传学首次被用来确定毒力基因在这种生长缓慢的厌氧细菌中的作用。
Dichelobacter nodosus is the essential causative agent of footrot in sheep. The major D. nodosus-encoded virulence factors that have been implicated in the disease are type IV fimbriae and extracellular proteases. To examine the role of the fimbriae in virulence, allelic exchange was used to insertionally inactivate the fimA gene, which encodes the fimbrial subunit protein, from the virulent type GD. nodosus strain VCS1703A. Detailed analysis of two independently derived fimA mutants revealed that they no longer produced the fimbrial subunit protein or intact fimbriae and did not exhibit twitching motility. In addition, these mutants were no longer capable of undergoing natural transformation and did not secrete wild-type levels of extracellular proteases. These effects were not due to polar effects on the downstream fimB gene because insertionally inactivated fimB mutants were not defective in any of these phenotypic tests. Virulence testing of the mutants in a sheep pen trial conducted under controlled environmental conditions showed that the fimA mutants were avirulent, providing evidence that the fimA gene is an essential D. nodosus virulence gene. These studies represent the first time that molecular genetics has been used to determine the role of virulence genes in this slow growing anaerobic bacterium.