Phenoloxidase and trypsin in germ-free larvae of Artemia fed with cooked unicellular diets: Examining the alimentary and protective effects of putative beneficial bacterium, yeast and microalgae against vibriosis

Three putative beneficial unicellular organisms, the marine bacterium Roseobacter sp, the yeast Saccharomyces cerevisiae mnn9 strain (SC-mnn9) and the microalga Tetraselmis suecica were cooked and offered separately as diets to developing germ-free (GF) Artemia larvae, in order to analyze their alimentary and protective effects. GF Artemia larvae were able to grow with cooked Tetraselmis and SC-mnn9 but failed with cooked Roseobacter. In spite of its high dietary quality, Tetraselmis failed to provide protection against Vibrio proteolyticus infection, while Roseobacter failed as food as well to provide protection. Cooked SC-mnn9 appeared to possess both values, dietary for growth and protective against Vibrio infection. GF Artemia larvae were apparently rapid adapted to dietary swaps; from yeast to algal and from algal to yeast. While the diets swap from algal or yeast, to bacterial diet appeared to be detrimental. Phenoloxidase-L (PO-L) and trypsin-L were used as biochemical indicators of defense and digestive functions, respectively. Developmental trypsin-L patterns were similar when fed on yeast and microalgae diets, suggesting a good digestive adaptation to plant or fungal substrates at early stages. On the contrary, diets swap or Vibrio infection affected PO-L and trypsin-L suggesting a sort of ‘alteration’ of digestive and defense functions.