Rathayibacter toxicus: how a bacterium hitches a ride on a nematode to invade grass seeds and produce a toxin harmful to livestock

Authors: Rogers, Elizabeth

Submitted to: Mid Atlantic Plant Molecular Biology Society Conference
Publication Type: Abstract Only
Publication Acceptance Date: 9/7/2017
Publication Date: 9/14/2017
Citation: Rogers, E.E. 2017. Rathayibacter toxicus: how a bacterium hitches a ride on a nematode to invade grass seeds and produce a toxin harmful to livestock. Mid Atlantic Plant Molecular Biology Society Conference . https://wp.towson.edu/mapms/files/2017/08.

Interpretive Summary:

Technical Abstract: Rathayibacter toxicus is a forage grass associated Gram-positive bacterium of major concern to food safety and agriculture. This species is listed by USDA-APHIS as a plant pathogen select agent because it produces a tunicamycin-like toxin that is lethal to livestock and may be vectored by nematode species native to the U.S. Our work with R. toxicus focuses on two major areas: diagnostic development and genetic characterization. Currently, we are developing antibodies that recognize either R. toxicus or tunicamycin itself as well as developing protocols for extracting and concentrating tunicamycin. To aid in genetic characterization, the complete genomes of two strains of R. toxicus, including the type strain FH-79, were sequenced, carefully annotated, and compared with two publically available R. toxicus genomes. Genome sizes ranged from 2,343,780 to 2,394,755 nucleotides, with 2079 to 2137 predicted open reading frames; all four strains showed remarkable synteny over nearly the entire genome, with only a small transposed region. A cluster of genes with similarity to the tunicamycin biosynthetic cluster from Streptomyces chartreusis was identified. The tunicamycin gene cluster (TGC) in R. toxicus contained 14 genes in two transcriptional units, with all of the functional elements for tunicamycin biosynthesis present. The TGC had a significantly lower GC content (52%) than the rest of the genome (61.5%), suggesting that the TGC may have originated from a horizontal transfer event. Further analysis indicated numerous remnants of other potential horizontal transfer events are present in the genome. In addition to the TGC, genes potentially associated with carotenoid and exopolysaccharide production, bacteriocins and secondary metabolites were identified. A CRISPR array is evident. There were relatively few plant-associated cell-wall hydrolyzing enzymes, but there were numerous secreted serine proteases that share sequence homology to the pathogenicity-associated protein Pat-1 of Clavibacter michiganensis. Current work focuses on genetic confirmation of the TGC function and on regulation of toxin biosynthesis.