Characterization of a Transferrable Pathogenicity Island in Streptomyces spp

Cornell Univ - State: Awds Made Prior May 2010, Ithaca NY

Investigators

Abstract

Horizontal gene transfer is an important mechanism for evolution of microbial pathogenicity of animals and plants. The specific genetic processes that lead to clustering and transfer of genes involved in pathogenicity of eucaryotic hosts are not well defined. Knowledge about these processes will allow us to determine how gene flow results in the emergence of new pathogens. This research addresses the role of horizontal gene transfer in the evolution of plant pathogenicity in the filamentous, Gram-positive genus Streptomyces. Horizontal transfer of a region containing a phytotoxin biosynthetic gene cluster txtAB and an independent virulence gene, nec1, and other virulence genes between pathogenic Streptomyces species appears to have resulted in the evolution of new pathogenic species in agricultural systems. There are several characteristics of these horizontally transferred regions that indicate association with a pathogenicity island (PAIS). PAIS are known to be important in the evolution of microbial pathogenicity, but have never been described in Gram-positive plant pathogens. Simultaneous transfer of both the nec1 and the txtAB regions from the recently described plant pathogen, S. turgidiscabies to S. lividans and several other nonpathogenic species has occurred in mating experiments. The recipient S. lividans strain has a pathogenicity phenotype. Preliminary data suggest that the putative PAIS may have been transferred on a giant plasmid. The specific objectives of the proposal are to: 1) Characterize the PAI and border regions in S. turgidiscabies; 2) Compare the genetic organization of the PAI and border regions in S. turgidiscabies to the PAIs in S. acidiscabies and S. scabies; and 3) Characterize the mechanism of transfer of the PAI from S. turgidiscabies into S. lividans. The work plan begins with an analysis of the transmissible PAI in S. turgidiscabies strain Car 8. The PAI is likely to be greater than 60 kb in size and contains the nec1 region, the txtAB region and other genes that are necessary for or facilitate pathogenicity. Large portions of the PAIs in the three species are identical in sequence, however, sequence deletions or insertions may be of biological significance and will be characterized. Border regions of the PAIs will shed light on the mechanism of transfer and target sequences. Analysis of the PAI sequences will reveal candidate pathogenicity and virulence ORFs as well as information about the kinds of recombination events that have occurred during the evolutionary history of the islands. This work will compliment research on evolution and mechanisms of pathogenicity in Gram-negative animal and plant pathogens and Gram-positive animal pathogens going on in other laboratories.