Involvement of N-acetylneuraminate cytidylyltransferase in Edwardsiella piscicida pathogenicity

Edwardsiella piscicida is a gram-negative bacterium that causes Edwardsiellosis in cultured fish. Edwardsiellosis is accompanied by symptoms such as skin lesions, hemorrhage, and necrosis in fish organs, which leads to significant economic losses in the aquaculture industry. Recently, we found that bacterial sialoglycoconjugates may be involved in the infectivity of E. piscicida. The more infectious strains of E. piscicida contain more sialic acid in the bacterial body, and the mRNA level of putative CMP-Neu5Ac synthase (css) is upregulated compared to that in the non-pathogenic strain. However, this putative css gene is yet to be cloned, and the involvement of CSS in E. piscicida pathogenicity remains unclear. Here, we cloned and transferred the css gene from E. piscicida into the FPC498 strain. CSS promoted infection in cultured cells originating from different fish species, and enhanced the mortality of E. piscicida-infected zebrafish larvae. CSS enhanced cell attachment and motility in E. piscicida, which differs from the decreased bacterial growth observed with the sialic acid-supplemented M9 medium. Both fractions (chloroform-methanol)-soluble and -insoluble fraction) prepared from E. piscicida pellet exhibited the increment of sialo-conjugates induced by CSS. Further, lectin blotting revealed the increment of Sia alpha 2-3- and alpha 2-6-, but not alpha 2 8 , -linked glycopmtein in CSS-overexpressing E. piscicida. Overall, these findings indicate the physiological significance of CSS and the role of sialylation in E. piscicida pathogenicity.

Automated summary

This study found that bacterial sialoglycoconjugates may be involved in the infectivity of Edwardsiella piscicida, a gram-negative bacterium that causes Edwardsiellosis in fish. Through cloning and transferring the css gene, the researchers discovered that CSS promotes infection and enhances mortality in infected zebrafish larvae. CSS also enhances bacterial attachment and motility and leads to an increase in sialo-conjugates.