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Evolution of the U.S. Biological Select Agent Rathayibacter toxicus
Edward W Davis1,2, Javier F Tabima1, Alexandra J Weisberg1
1Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA.
Mbio
|August 30, 2018
Summary
Rathayibacter toxicus, a toxin-producing bacterium, exhibits low genetic diversity due to a dramatic evolutionary event involving bacteriophages and a CRISPR system. This study reveals insights into its genome reduction and ecological adaptations.
Area of Science:
- Microbiology
- Evolutionary Biology
- Genomics
Background:
- Rathayibacter toxicus causes annual ryegrass toxicity, a fatal disease in grazing animals.
- This bacterium is a regulated species in the US due to its potential threat.
Purpose of the Study:
- To model the evolution of R. toxicus using phylogenomics.
- To explain the low genetic diversity observed in R. toxicus isolates.
- To provide taxonomic insights into the Rathayibacter genus.
Main Methods:
- Phylogenomic analysis of over 100 Rathayibacter genomes.
- Characterization of CRISPR spacers to reconstruct infection history.
- Comparative genomic analysis to study genome reduction and diversity.
Main Results:
- Rathayibacter genus comprises nine species-level groups.
- R. toxicus is genetically distinct, showing significant genome reduction.
- Low intergroup and intragroup genomic diversity was observed in R. toxicus.
- R. toxicus is unique in possessing a CRISPR locus and a bacteriophage parasite.
Conclusions:
- A three-stage evolutionary process involving bacteriophages and CRISPR explains R. toxicus genome reduction and low diversity.
- Coexistence with bacteriophage NCPPB3778 likely drove genome shrinkage and species divergence.
- This research enhances understanding of the evolution and ecology of R. toxicus.
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