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J. Bacteriol., Sep 1997, 5292-5299, Vol 179, No. 17
E Umelo and TJ Trust
Two tandemly located flagellin genes, flaA and flaB, with 79% nucleotide
sequence identity were identified in Aeromonas salmonicida A449. The fla
genes are conserved in typical and atypical strains of A. salmonicida, and
they display significant divergence at the nucleotide level from the fla
genes of the motile species Aeromonas hydrophila and Aeromonas veronii
biotype sobria. flaA and flaB encode unprocessed flagellins with predicted
Mrs of 32,351 and 32,056, respectively. When cloned under the control of
the Ptac promoter, flaB was highly expressed when induced in Escherichia
coli DH5alpha, and the FlaB protein was detectable even in the uninduced
state. In flaA clones containing intact upstream sequence, FlaA was barely
detectable when uninduced and poorly expressed on induction. The A.
salmonicida flagellins are antigenically cross-reactive with the A.
hydrophila TF7 flagellin(s) and evolutionarily closely related to the
flagellins of Pseudomonas aeruginosa and Vibrio anguillarum. Electron
microscopy showed that A. salmonicida A449 expresses unsheathed polar
flagella at an extremely low frequency under normal laboratory growth
conditions, suggesting the presence of a full complement of genes whose
products are required to make flagella; e.g., immediately downstream of
flaA and flaB are open reading frames encoding FlaG and FlaH homologs.
Copyright © 1997, American Society for Microbiology
Identification and molecular characterization of two tandemly located flagellin genes from Aeromonas salmonicida A449
Department of Biochemistry and Microbiology and Canadian Bacterial Diseases Network, University of Victoria, British Columbia, Canada.
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