Francisella noatunensis modulates the hepatic profile of fatty acids in Patagonian blennie Eleginops maclovinus

Fatty acids (FA) have been reported to play a role in the defense against bacterial pathogens. However, studies in fish are limited and no information exists on the modulation of FA of Eleginops maclovinus challenged with the pathogen of aquaculture relevance Francisella noatunensis. We inoculated 144 fish intraperitoneally with 3 doses (low dose [LD]: 1 x 101 bact/mu L; medium dose [MD]: 1 x 105 bact/mu L; high dose [HD]: 1 x 1010 bact/mu L) and a control dose (sterile culture medium, [C]) of the bacteria F. noatunensis and took liver samples at 1, 3, 7, 14, 21, 28 days post-inoculation (dpi). The LD of F. noatunensis did not present significant differences to the C, except for the C20:4n6 (ARA) at day 28, while the MD and HD of F. noatunensis did generate a significant effect of the FA profile of E. maclovinus. We observed a greater modulation after administering the HD of bacteria and detected significant differences from day 3 post-inoculation (P < 0.05). Significantly high levels of C18:0 was detected at day 28 (P < 0.05), while significantly low levels of C14:0, C20:0, C16:1, C18:1n9, C18:2n6; C18:3n3, and C20:5n3 were detected at different dpi of F. noatunensis (P < 0.05). ARA and C22:6n3 (DHA) showed a significant decrease during the first dpi (P < 0.05) but later they showed an increase in their levels, with ARA increasing its levels from day 14 (P < 0.05), while DHA increased its levels only at day 28 (P < 0.05). A large number of FA were highly correlated with each other and multivariate statistical analyzes (PCA and random forest) were able to detect the HD of F. noatunensis as the dose that most affects the FA profile of E. maclovinus, while the LD, MD and C cannot be differentiated in their FA profile. The FA most affected by the challenge with F. noatunensis were C18:2n3 and C18:3n3 (P < 0.05). Our results suggest a relationship between the bioavailability of FA in the liver and the level of the physiological response of E. maclovinus to an experimental challenge with F. noatunensis and suggest that hepatic FA modulation may explain or be part of the high tolerance to bacterial infections reported for E. maclovinus, although more studies are necessary to clarify the roles of the different types of FA on pathogen-host dynamics and its potential use in combating fish pathogenic bacteria.

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