Sea Bass Immunization to Downsize the Betanodavirus Protein Displayed in the Surface of Inactivated Repair-Less Bacteria

This work describes immunization of European sea bass (Dicentrarchus labrax) juveniles against viral nervous necrosis virus (VNNV), a betanodavirus causing worldwide mortalities in many fish species. Protection was obtained with the so-called spinycterin vehicles consisting of irreversibly DNA-damaged DNA-repair-less Escherichia coli 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(91-220)) containing most of its previously determined antigenicity, (ii) developed a scalable autoinduction culture media for E. coli based in soy-bean rather than in casein hydrolysates, (iii) enriched surface expression by screening different anchors from several prokaryotic sources (anchor + frgC(91-220) recombinant products), (iv) preserved frgC(91-220) antigenicity by inactivating bacteria by irreversible DNA-damage by means of Ciprofloxacin, and (v) increased safety using a repair-less E. coli strain as chassis for the spinycterins. These spinycterins protected fish against VNNV challenge with partial (Nmistic + frgC(91-220)) or total (YBEL + frgC(91-220)) levels of protection, in contrast to fish immunized with frgC(91-220) spinycterins(.) 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.