Dissertation > Agricultural Sciences > Plant Protection > Pest and Disease Control > Plant diseases and their prevention > Transgression ( pass ) an infectious agent harmful

A Primary Study of Quorum Sensing in Erwinia Amylovora

Author GaoYan
Tutor LiuFengQuan;HuBaiShi
School Nanjing Agricultural College
Course Plant Pathology
Keywords Erwinia amylovora Quorum sensing luxS luxR PCR molecular detection
CLC S432.4
Type Master's thesis
Year 2006
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Fire blight, caused by Erwinia amylovora, is one of the most devastating and difficult-to-control diseases. To control this disease effectually, research has been focused on the molecular mechanisms of the virulence. While the production of virulence factors in many phytopathogenic bacteria is regulated by Quorum Sensing(QS).In this study, we cloned for the first time the homolog of luxS, related to the biosynthesis of AI-2 in Er. amylovora. By the Vibrio harveyi luminescence bioassay, it was found that Er. amylovora strain 0056 could synthesize AI-2: the maximum functional AI-2 activity occurred during late-exponential growth phases and diminished during stationary phase. The highest levels of AI-2 were observed in NB medium, compared with AB and LB medium. The expression of luxS orthologue of Er. amylovora in Escherichia coli DH5a cells deficient in luxS, restored AI-2 activity to these cells. To evaluate whether luxS ortholog is essential for AI-2 synthesis further, the ΔluxS mutant in Er. amylovora strain 0056 has been constructed, and it showed no functional AI-2 activity. But the mutant still infected the unmatured pears. So it showed that AI-2 had no effect on the pathogen’s infection of unmatured pears. While growth defect of the mutant was showed in NB medium compared with wide-type strain 0056. The mutant couldn’t grow when coculture of the mutant and wide-type strain 0056. We deduced primarily that AI-2 might affect environmental fitness of Er. amylovora .SdiA, belongs to luxR family involved in QS, are present in Es. coli and Salmonella typhimurium genome. In this report, a homolog of sdiA was cloned from Er. amylovora , which shares 45.42% amino acid identity (69.58% similarity) with Es. coli and 43.33% (67.08% similarity) of S. typhimurium. Southern blot analysis of the luxR-homolog of Er. amylovora with a DNA probe indicated it was two copies in the genome of Er. amylovora strain 0056. In addition, according to regions of luxR-homolog in Er. amylovora where divergent from other luxR-homolog reported, specific primers F-EA and D-EA were designed to identify Er. amylovra. Ten tested Er. amylovra strains were successfully identified using the primers from a range of closely related bacteria. And it was proved to be highly sensitive with 10 colony forming units (cfu). Moreover, it successfully detected

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