Among their numerous physiological effects, heat shock proteins (Hsps) are potent immunomodulators, a characteristic reflecting their potential as therapeutic agents and which led to their application in combating infection. As an example, the up-regulation of endogenous Hsp70 in the branchiopod crustacean Artemia franciscana (Kellogg) is concurrent with shielding against bacterial infection. To better understand this protective mechanism, gnotobiotic Artemia were fed with Escherichia coli treated to over-produce different prokaryotic Hsps. This was shown to increase larval resistance to experimental Vibrio campbellii exposure. Immunoprobing of Western blots showed that the enhanced resistance to V. campbellii correlated with DnaK production in E coli. A definitive role for DnaK was then demonstrated by feeding Artemia larvae with transformed bacteria over-producing only this protein, although other Hsps such as DnaJ and grpE also provided tolerance against Vibrio infection. Feeding of bacteria synthesizing selected Hsps is therefore suggested as an alternative to antibiotic use as a means of enhancing resistance of Artemia larvae to bacterial infection, which may have potential applications in aquaculture.
Feeding of bacterially encapsulated heat shock proteins (Hsps) to invertebrates is a novel way to limit Vibrio infection. As an example, ingestion of Escherichia coli overproducing prokaryotic Hsps significantly improves survival of gnotobiotically cultured Artemia larvae upon challenge with pathogenic Vibrio campbellii. The relationship between Hsp accumulation and enhanced resistance to infection may involve DnaK, the prokaryotic equivalent to Hsp70, a major molecular chaperone in eukaryotic cells. In support of this proposal, heat-stressed bacterial strains LVS 2 (Bacillus sp.), LVS 3 (Aeromonas hydrophila), LVS 8 (Vibrio sp.), GR 8 (Cytophaga sp.), and GR 10 (Roseobacter sp.) were shown in this work to be more effective than nonheated bacteria in protecting gnotobiotic Artemia larvae against V. campbellii challenge. Immunoprobing of Western blots and quantification by enzyme-linked immunosorbent assay revealed that the amount of DnaK in bacteria and their ability to enhance larval resistance to infection by V. campbellii are correlated. Although the function of DnaK is uncertain, it may improve tolerance to V. campbellii via immune stimulation, a possibility of significance from a fundamental perspective and also because it could be applied in aquaculture, a major method of food production.