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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #219389

Title: Characterization of the RRN Operons in the Channel Catfish Pathogen Edwardsiella ictaluri

item Williams, M
item Waldbieser, Geoffrey - Geoff
item Dyer, D
item Gillaspy, A
item Lawrence, M

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2007
Publication Date: 11/22/2007
Citation: Williams, M., Waldbieser, G.C., Dyer, D.W., Gillaspy, A.F., Lawrence, M.L. 2008. Characterization of the RRN Operons in the Channel Catfish Pathogen Edwardsiella ictaluri. Journal of Applied Microbiology 104:1790-1796.

Interpretive Summary: Edwardsiella ictaluri is the causative pathogen of Enteric Septicemia of Catfish, a major cause of mortalities in commercial catfish production. In order to better understand the nature of this bacteria and its relationships with other bacteria in the family Enterobacteriaceae, the DNA sequences were identified that encode the ribosomal RNA (rrn) gene groups (operons). The DNA sequences of rrn operons and the regions flanking them were similar between E. ictaluri and other Enterobacteriaceae, however, the presence of eight copies of the rrn operon made E. ictaluri unique within the family. This information provided DNA sequence with the potential for use in diagnostic tests, and also provided sequence and structural information to support the E. ictaluri genome sequencing project.

Technical Abstract: Aims: To advance diagnostics and phylogenetics of Edwardsiella ictaluri by sequencing and characterizing its rrn operons. Methods and Results: The Edw. ictaluri rrn operons were identified from a 5-7 kb insert lambda library and from Edw. ictaluri fosmid clones. We present the complete sequences and analysis of all eight Edw. ictaluri rrn operons and unique regions located upstream and downstream. Two rrn operons were located in tandem with 169 bp separating them, which is apparently a conserved feature between Edw. ictaluri and Edw. tarda. I-CeuI enzyme digestion of Edw. ictaluri genomic DNA and analysis by pulsed field gel electrophoresis indicated that rrn operon number and chromosomal locations are conserved within the species Edw. ictaluri. Conclusions: The rrn operons of Edw. ictaluri have similar structure and flanking regions compared to other members of the family Enterobacteriaceae; however, the presence of eight copies of the rrn operon makes Edw. ictaluri unique within the family. Significance and Impact of the Study: This research clarifies previous phylogenetic analyses of Edw. ictaluri and provides support for the Edw. ictaluri genome sequencing project. In addition, we identified a unique feature of two rrn operons that shows potential for development of a diagnostic PCR method.