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Comparative genomics of Riemerella anatipestifer reveals genetic diversity.

ABSTRACT: BACKGROUND: Riemerella anatipestifer is one of the most important pathogens of ducks. However, the molecular mechanisms of R. anatipestifer infection are poorly understood. In particular, the lack of genomic information from a variety of R. anatipestifer strains has proved severely limiting. RESULTS: In this study, we present the complete genomes of two R. anatipestifer strains, RA-CH-1 (2,309,519 bp, Genbank accession CP003787) and RA-CH-2 (2,166,321 bp, Genbank accession CP004020). Both strains are from isolates taken from two different sick ducks in the SiChuang province of China. A comparative genomics approach was used to identify similarities and key differences between RA-CH-1 and RA-CH-2 and the previously sequenced strain RA-GD, a clinical isolate from GuangDong, China, and ATCC11845. CONCLUSION: The genomes of RA-CH-2 and RA-GD were extremely similar, while RA-CH-1 was significantly different than ATCC11845. RA-CH-1 is 140,000 bp larger than the three other strains and has 16 unique gene families. Evolutionary analysis shows that RA-CH-1 and RA-CH-2 are closed and in a branch with ATCC11845, while RA-GD is located in another branch. Additionally, the detection of several iron/heme-transport related proteins and motility mechanisms will be useful in elucidating factors important in pathogenicity. This information will allow a better understanding of the phenotype of different R. anatipestifer strains and molecular mechanisms of infection.

SUBMITTER: Wang X

PROVIDER: S-EPMC4103989 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Comparative genomics of Riemerella anatipestifer reveals genetic diversity.

Wang Xiaojia X Liu Wenbin W Zhu Dekang D Yang LinFeng L Liu MaFeng M Yin Sanjun S Wang MingShu M Jia RenYong R Chen Shun S Sun KunFeng K Cheng Anchun A Chen Xiaoyue X

BMC genomics 20140617

<h4>Background</h4>Riemerella anatipestifer is one of the most important pathogens of ducks. However, the molecular mechanisms of R. anatipestifer infection are poorly understood. In particular, the lack of genomic information from a variety of R. anatipestifer strains has proved severely limiting.<h4>Results</h4>In this study, we present the complete genomes of two R. anatipestifer strains, RA-CH-1 (2,309,519 bp, Genbank accession CP003787) and RA-CH-2 (2,166,321 bp, Genbank accession CP004020) ...[more]

PMID: 24935762

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Project description:Duck infectious serositis, also known as Riemerella anatipestifer disease, infects domestic ducks, geese, and turkeys and wild birds. However, the regulatory mechanism of its pathogenicity remains unclear. The PhoPR two-component system (TCS) was first reported in Gram-negative bacteria in our previous research and was demonstrated to be involved in virulence and gene expression. Here, DNA affinity purification sequencing (DAP-seq) was applied to further explore the regulation of PhoPR in relation to pathogenicity in R. anatipestifer. A conserved motif was identified upstream of 583 candidate target genes which were directly regulated by PhoP. To further confirm the genes which are regulated by PhoR and PhoP, single-gene-deletion strains were constructed. The results of transcriptome analysis using next-generation RNA sequencing showed 136 differentially expressed genes (DEGs) between the ΔphoP strain and the wild type (WT) and 183 DEGs between the ΔphoR strain and the WT. The candidate target genes of PhoP were further identified by combining transcriptome analysis and DAP-seq, which revealed that the main direct regulons of PhoP are located on the membrane and PhoP is involved in regulating aerotolerance. Using the in vivo duck model, the pathogenicity of ΔphoP and ΔphoR mutants was found to be significantly lower than that of the WT. Together, our findings provide insight into the direct regulation of PhoP and suggest that phoPR is essential for the pathogenicity of R. anatipestifer. The gene deletion strains are expected to be candidate live vaccine strains of R. anatipestifer which can be used as ideal genetic engineering vector strains for the expression of foreign antigens. IMPORTANCE Riemerella anatipestifer is a significant pathogen with high mortality in the poultry industry that causes acute septicemia and infectious polyserositis in ducks, chickens, geese, and other avian species. Previously, we characterized the two-component system encoded by phoPR and found that R. anatipestifer almost completely lost its pathogenicity for ducklings when phoPR was deleted. However, the mechanism of PhoPR regulation of virulence in R. anatipestifer had not been deeply explored. In this study, we utilized DAP-seq to explore the DNA-binding sites of PhoP as a response regulator in the global genome. Furthermore, phoP and phoR were deleted separately, and transcriptomics analysis of the corresponding gene deletion strains was performed. We identified a series of directly regulated genes of the PhoPR two-component system. The duckling model showed that both PhoP and PhoR are essential virulence-related factors in R. anatipestifer.

Project description:Riemerella anatipestifer is an important pathogen in waterfowl, and is generally multidrug resistant. This study assessed the current status of Riemerella anatipestifer antibiotic resistance and antibiotic-resistance genes (ARGs), compared the results of different detection methods, and evaluated a new method of studying the association between antibiotic resistance and ARGs in Riemerella anatipestifer. In this study, 51 strains of Riemerella anatipestifer were isolated from ducks on several farms, their resistance to 28 antibiotics was assessed, and the isolates were subjected to whole-genome sequencing. The number of ARGs carried by Riemerella anatipestifer was predicted, compared, and analyzed, and the consistency between ARGs and antibiotic-resistance phenotypes was assessed. The potential for loss of resistance genes during the sequencing and assembly of genome-wide framework map was assessed, and a new ARG detection method was pilot tested. The 51 strains of Riemerella anatipestifer were multidrug resistant (MDR) and had high level of resistance to aminoglycosides, trimethoprim, lincosamides, polypeptides, and macrolides. Based on the genome-wide framework map of the 51 strains, 3 local databases of ABRicate software and 1 online database of CARD website were used to detect ARGs, and a mean of 4 to 5 ARGs were identified per isolate. Although the detection results differed according to the database used, the general performance was consistent. The online website detected more types of ARGs than the ABRicate software. The association between ARGs and antibiotic-resistance phenotypes was assessed, and the ermF gene was identified as a possible key ARGs regulating macrolide resistance of Riemerella anatipestifer. The method used to investigate and detect Riemerella anatipestifer ARGs was convenient and rapid, and had strong accuracy and pertinence. The ARGs detection method reported here combined the advantages of PCR and genome detection, and could greatly reduce workload and detect ARGs more precisely.

Project description:BackgroundRiemerella anatipestifer (R. anatipestifer) is one of the most important poultry pathogens worldwide, with associated infections causing significant economic losses. Rifampin Resistance is an important mechanism of drug resistance. However, there is no information about rpoB mutations conferring rifampin resistance and its fitness cost in Riemerella anatipestifer.ResultsComparative analysis of 18 R.anatipestifer rpoB sequences and the determination of rifampin minimum inhibitory concentrations showed that five point mutations, V382I, H491N, G502K, R494K and S539Y, were related to rifampin resistance. Five overexpression strains were constructed using site-directed mutagenesis to validate these sites. To investigate the origin and fitness costs of the rpoB mutations, 15 types of rpoB mutations were isolated from R. anatipestifer ATCC 11845 by using spontaneous mutation in which R494K was identical to the type of mutation detected in the isolates. The mutation frequency of the rpoB gene was calculated to be 10- 8. A total of 98.8% (247/250) of the obtained mutants were located in cluster I of the rifampin resistance-determining region of the rpoB gene. With the exception of D481Y, I537N and S539F, the rifampin minimum inhibitory concentrations of the remaining mutants were at least 64 μg/mL. The growth performance and competitive experiments of the mutant strains in vitro showed that H491D and 485::TAA exhibit growth delay and severely impaired fitness. Finally, the colonization abilities and sensitivities of the R494K and H491D mutants were investigated. The sensitivity of the two mutants to hydrogen peroxide (H2O2) and sodium nitroprusside (SNP) increased compared to the parental strain. The number of live colonies colonized by the two mutants in the duckling brain and trachea were lower than that of the parental strain within 24 h.ConclusionsMutations of rpoB gene in R. anatipestifer mediate rifampin resistance and result in fitness costs. And different single mutations confer different levels of fitness costs. Our study provides, to our knowledge, the first estimates of the fitness cost associated with the R. anatipestifer rifampin resistance in vitro and in vivo.

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Comparative genomics of Riemerella anatipestifer reveals genetic diversity.

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Comparative genomics of Riemerella anatipestifer reveals genetic diversity.

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