Dataset Information

Whole genome sequence of two Rathayibacter toxicus strains reveals a tunicamycin biosynthetic cluster similar to Streptomyces chartreusis.

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. The complete genomes of two strains of R. toxicus, including the type strain FH-79, were sequenced and analyzed in comparison with all available, complete 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. Overall, the genome provides clear insight into the possible mechanisms for toxin production in R. toxicus, providing a basis for future genetic approaches.

SUBMITTER: Sechler AJ

PROVIDER: S-EPMC5552033 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Rathayibacter toxicus is a species of Gram-positive, corynetoxin-producing bacteria that causes annual ryegrass toxicity, a disease often fatal to grazing animals. A phylogenomic approach was employed to model the evolution of R. toxicus to explain the low genetic diversity observed among isolates collected during a 30-year period of sampling in three regions of Australia, gain insight into the taxonomy of Rathayibacter, and provide a framework for studying these bacteria. Analyses of a data set of more than 100 sequenced Rathayibacter genomes indicated that Rathayibacter forms nine species-level groups. R. toxicus is the most genetically distant, and evidence suggested that this species experienced a dramatic event in its evolution. Its genome is significantly reduced in size but is colinear to those of sister species. Moreover, R. toxicus has low intergroup genomic diversity and almost no intragroup genomic diversity between ecologically separated isolates. R. toxicus is the only species of the genus that encodes a clustered regularly interspaced short palindromic repeat (CRISPR) locus and that is known to host a bacteriophage parasite. The spacers, which represent a chronological history of infections, were characterized for information on past events. We propose a three-stage process that emphasizes the importance of the bacteriophage and CRISPR in the genome reduction and low genetic diversity of the R. toxicus species.IMPORTANCERathayibacter toxicus is a toxin-producing species found in Australia and is often fatal to grazing animals. The threat of introduction of the species into the United States led to its inclusion in the Federal Select Agent Program, which makes R. toxicus a highly regulated species. This work provides novel insights into the evolution of R. toxicusR. toxicus is the only species in the genus to have acquired a CRISPR adaptive immune system to protect against bacteriophages. Results suggest that coexistence with the bacteriophage NCPPB3778 led to the massive shrinkage of the R. toxicus genome, species divergence, and the maintenance of low genetic diversity in extant bacterial groups. This work contributes to an understanding of the evolution and ecology of an agriculturally important species of bacteria.

Project description:Rathayibacter toxicus is a gram-positive bacterium that infects the floral parts of several Poaceae species in Australia. Bacterial ooze is often produced on the surface of infected plants and bacterial galls are produced in place of seed. R. toxicus is a regulated plant pathogen in the U.S. yet reliable detection and diagnostic tools are lacking. To better understand this geographically-isolated plant pathogen, genetic variation as a function of geographic location, host species, and date of isolation was determined for isolates collected over a forty-year period. Discriminant analyses of recently collected and archived isolates using Multi-Locus Sequence Typing (MLST) and Inter-Simple Sequence Repeats (ISSR) identified three populations of R. toxicus; RT-I and RT-II from South Australia and RT-III from Western Australia. Population RT-I, detected in 2013 and 2014 from the Yorke Peninsula in South Australia, is a newly emerged population of R. toxicus not previously reported. Commonly used housekeeping genes failed to discriminate among the R. toxicus isolates. However, strategically selected and genome-dispersed MLST genes representing an array of cellular functions from chromosome replication, antibiotic resistance and biosynthetic pathways to bacterial acquired immunity were discriminative. Genetic variation among isolates within the RT-I population was less than the within-population variation for the previously reported RT-II and RT-III populations. The lower relative genetic variation within the RT-I population and its absence from sampling over the past 40 years suggest its recent emergence. RT-I was the dominant population on the Yorke Peninsula during the 2013-2014 sampling period perhaps indicating a competitive advantage over the previously detected RT-II population. The potential for introduction of this bacterial plant pathogen into new geographic areas provide a rationale for understanding the ecological and evolutionary trajectories of R. toxicus.

Dataset Information

Whole genome sequence of two Rathayibacter toxicus strains reveals a tunicamycin biosynthetic cluster similar to Streptomyces chartreusis.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets