Virulence mechanisms of plant pathogenic Streptomyces species

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Potato common scab is an important plant disease that occurs in many potato growing regions in Canada. The disease is characterized by superficial or raised corky-like lesions that form on the surface of the potato tuber. These lesions affect the marketability of the potato crop leading to significant economic losses for potato growers. In 2002, the total economic loss to potato scab in Canada was estimated to be between $15-17 million dollars, highlighting the importance of this disease to the Canadian potato industry and the economy as a whole. A causative agent of common scab is a soil-dwelling, filamentous bacterium called Streptomyces scabies. The disease symptoms induced by this organism are mainly due to production of a phytotoxin called thaxtomin A, which functions as a cellulose synthesis inhibitor. In addition, other known or putative virulence determinants have been identified that are thought to contribute to the severity of disease symptoms caused by S. scabies. The short-term goal of this research is to characterize the product of a newly-discovered secondary metabolite biosynthetic cluster that is important for virulence in S. scabies. The metabolite will be purified from S. scabies cultures so that its structure can be determined and its contribution to disease symptom development can be assessed. In addition, the biosynthesis of this metabolite will be examined through construction of S. scabies gene deletions. The results of this study will provide important insight into the molecular mechanisms of pathogenicity in S. scabies, which is the long-term goal of this research. It is anticipated that the information gained will lead to a better understanding of scab disease development in agricultural settings and may suggest more effective ways of controlling it and the pathogens that cause it. In addition, this research will benefit Canada by training students in techniques that will allow them to pursue successful research careers at academic institutions or in government or industry labs.