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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI:

    Francisellosis of Yesso scallops Mizuhopecten yessoensis in Japan is caused by a novel type of Francisella halioticida

    Miku Kawahara, Kazutoshi Yoshitake, Tomoyoshi Yoshinaga, Naoki Itoh*

    *Corresponding author:

    ABSTRACT: Francisella halioticida, known as the causative agent of francisellosis of the giant abalone, has been isolated from Yesso scallops Mizuhopecten yessoensis, which presented with orange/pinkish lesions in the addcutor muscle and high mortality. However, it is not clear whether the F. halioticida isolated from the giant abalone and Yesso scallops are phenotypically and genetically identical to each other. The present study revealed that isolates from the giant abalone and Yesso scallops were phenotypically different, with slower growth in modified eugon broth and a lack of prolyl aminopeptidase and phenylalanine aminopeptidase in Yesso scallop isolates. Additionally, we found that 3 of 8 housekeeping genes were different between them. Based on these phenotypic and genetic differences, we propose that F. halioticida isolated from Yesso scallops in Japan be designated as the J-scallop type to distinguish it from strains from abalone (abalone type). Whole-genome sequencing analysis of a strain belonging to the J-scallop type showed that the overall similarity between the J-scallop and abalone type strains was estimated as 99.84%. In accordance with a lack of prolyl aminopeptidase activity, in general, all the J-scallop type strains examined have a 1 bp deletion in the responsible prolyl aminopeptidase gene. Later, this deletion was confirmed in all the F. halioticida in diseased Yesso scallops examined, suggesting that in Japan, francisellosis of Yesso scallops is caused by a novel type of F. halioticida and not the abalone type.