Research InterestsI am interested in a diverse and fascinating group of microorganisms called the streptomycetes, which are Gram-positive, filamentous bacteria that are ubiquitous in the environment. These microorganisms are known for their large, GC-rich, linear chromosomes and for their complex developmental life cycle that involves the formation of aerial hyphae structures and chains of spores. In addition, Streptomyces species are renowned for their ability to produce medically- and agriculturally- important secondary metabolites such as antibiotics, anti-viral, anti-fungal, herbicidal and immunosuppressive compounds. In fact, over two-thirds of the clinically-important natural products currently in use are produced by the streptomycetes! Most Streptomyces species are saphrophytes that degrade complex organic polymers and contribute to nutrient recycling in the environment. However, there are some species that also have the ability to infect living plant tissue and are the causative agents of economically-important crop diseases such as potato common scab.
Current research projects in the Bignell lab:
(I) Virulence mechanisms of plant pathogenic Streptomyces species. Of the 500 or more Streptomyces species that have been identified, only about a dozen or so have the ability to cause disease on plants. The oldest plant pathogenic species, S. scabies, causes common scab disease, which is characterized by corky-like lesions that form on the potato tuber surface. These lesions affect the marketability of the potato crop and result in significant economic losses to potato growers. Other economically-important root crops are also susceptible to S. scabies infection including radish, beet, turnip and carrot.
Scab disease symptoms on a potato tuber. Image courtesy of M. Joshi, Cornell University.
Colonization of radish seedling roots by GFP-labeled S. scabies.
My lab is interested in determining the molecular mechanisms used by S. scabies and other scab-causing streptomycetes to cause disease on plants. In particular, we are interested in characterizing the secondary metabolites that are produced by pathogenic species and which contribute to the virulence phenotype. Recently, a novel polyketide biosynthetic gene cluster was identified in the genome sequence of S. scabies 87-22. This cluster is predicted to synthesize metabolites that are similar to the coronatine (COR) phytotoxin that is produced by the Gram-negative plant pathogen, Pseudomonas syringae. Research in my lab will focus on (a) determining the chemical structure of the S. scabies metabolites, (b) characterizing the biosynthesis of the metabolites, and (c) assessing the contribution of the metabolites to disease symptom development and host-pathogen interactions.
Structure of the COR phytotoxin
produced by P. syringae.
(II) Regulation of tylosin production by Streptomyces fradiae.