| Summary: | This work describes immunization of European sea bass (<i>Dicentrarchus labrax</i>) juveniles against viral nervous necrosis virus (VNNV), a <i>betanodavirus</i> causing worldwide mortalities in many fish species. Protection was obtained with the so-called spinycterin vehicles consisting of irreversibly DNA-damaged DNA-repair-less <i>Escherichia coli</i> displaying at their surface a downsized VNNV coat antigen. In this work we have (i) maximized bacterial expression levels by downsizing the coat protein of VNNV to a fragment (frgC<sub>91−220</sub>) containing most of its previously determined antigenicity, (ii) developed a scalable autoinduction culture media for <i>E. coli</i> based in soy-bean rather than in casein hydrolysates, (iii) enriched surface expression by screening different anchors from several prokaryotic sources (anchor + frgC<sub>91−220</sub> recombinant products), (iv) preserved frgC<sub>91−220</sub> antigenicity by inactivating bacteria by irreversible DNA-damage by means of Ciprofloxacin, and (v) increased safety using a repair-less <i>E. coli</i> strain as chassis for the spinycterins. These spinycterins protected fish against VNNV challenge with partial (Nmistic + frgC<sub>91−220</sub>) or total (YBEL + frgC<sub>91−220</sub>) levels of protection, in contrast to fish immunized with frgC<sub>91−220</sub> spinycterins<sub>.</sub> The proposed spinycterin platform has high levels of environmental safety and cost effectiveness and required no adjuvants, thus providing potential to further develop VNNV vaccines for sustainable aquaculture.
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