|Van Santen, Vicky|
Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2009
Publication Date: 6/30/2009
Publication URL: http://hdl.handle.net/10113/43763
Citation: Panangala, V.S., Russo, R., Van Santen, V.L., Wolfe, K.G., Klesius, P.H. 2009. Organization and sequence of four flagellin-encoding genes of Edwardsiella icataluri. Aquaculture Research. 40:1135-1147. Interpretive Summary: Edwardsiella ictaluri the cause of enteric septicemia in channel catfish (Ictalurus punctatus) ranks as the most important bacterial fish pathogen in warmwater aquaculture industry in the United States and throughout the world. Mortality from enteric septicemia (ESC) could range from 50 – 60 % annually in the USA particularly among catfish fingerlings and food-size fish. In monitory terms losses from ESC range between $ 50 to $ 60 million annually to the catfish industry. As at the present time, little or no information is available on the virulence mechanisms of E. ictaluri and only sparse information is available at the molecular genetic level on the mechanisms of pathogenesis, an area upon which high priority has been placed in the National Program (NP-106) component II, subsection (d) Mechanisms of Disease and (f) Microbial Genomics. In this study, we discovered the complete nucleotide and amino acid sequences of four flagellin genes of E. ictaluri for the first time. The flagella are considered to be an extremely important virulence factor of this organism, by means of which the organism is able to sense, and respond to external stimuli and propel to a preferred habitat niche in the catfish host. These flagella proteins bear dominant antigenic epitopes which stimulate an antibody response in the catfish and are hence important in the immune response of the host. The antigens could be potential vaccine candidates that could be used in future vaccine development for protection against ESC disease.
Technical Abstract: Edwardsiella ictaluri, the cause of enteric septicemia in channel catfish (Ictalurus punctatus), is motile by means of peritrichous flagella. We determined the complete flagellin gene sequences and their organization in E. ictaluri by sequencing genomic segments selected from a lambda-ZAP phage genomic library of E. ictaluri. Four flagellin genes (fliC1, fliC2, fliC3, fliC4) are arranged in tandem within 6 kb in the E. ictaluri genome. Each flagellin coding sequence is preceded by a Sigma 28 recognition site consensus sequence. FliC2, fliC3, and fliC4 are separated by < 300 nt. In contrast, fliC1 and fliC2 are separated by 1.1 kb, which include a 172-codon ORF with homology to the amino terminal portion of a mutator-type transposase distinct from the E. ictaluri TnpA. The predicted amino acid sequences of all four flagellin proteins are similar in the N-terminal (aa 1-160) and C-terminal (last 74 aa) portions and are divergent in the central portion of the proteins. Proteins encoded by the fliC1, fliC2, and fliC3 are more similar to each other (88-90% aa identity) than to the protein encoded by fliC4 (76-78% identity). The predicted sizes of the encoded proteins range between 36 and 37.5 kDa and are in good agreement with the flagellin peptides (~35-37 kDa) resolved by SDS-PAGE. BLAST analysis of GenBank sequences showed that all four flagellin aa sequences are more similar to those of Serratia marcescens (72-74% identity) than to those of Edwardsiella tarda (is less than or equal to 64% identity). Primary determination of E. ictaluri flagellin gene sequences will lend to advance our studies on the role of flagella in host-pathogen interaction.