Influence of different yeast cell-wall mutants on performance and protection against pathogenic bacteria (Vibrio campbellii) in gnotobiotically-grown Artemia.

A selection of isogenic yeast strains (with deletion for genes involved in cell-wall synthesis) was used to evaluate their nutritional and immunostimulatory characteristics for gnotobiotically-grown Artemia. In the first set of experiments the nutritional value of isogenic yeast strains (effected in mannoproteins, glucan, chitin and cell-wall bound protein synthesis) for gnotobiotically-grown Artemia was studied. Yeast cell-wall mutants were always better feed for Artemia than the isogenic wild type mainly because they supported a higher survival but not a stronger individual growth. The difference in Artemia performance between WT and mutants feeding was reduced when stationary-phase grown cells were used. These results suggest that any mutation affecting the yeast cell-wall make-up is sufficient to improve the digestibility in Artemia. The second set of experiments, investigates the use of a small amount of yeast cells in gnotobiotic Artemia to overcome pathogenicity of Vibrio campbellii (VC). Among all yeast cell strains used in this study, only mnn9 yeast (less cell-wall bound mannoproteins and more glucan and chitin) seems to completely protect Artemia against the pathogen. Incomplete protection against the pathogen was obtained by the gas1 and chs3 mutants, which are lacking the gene for a particular cell-wall protein and chitin synthesis, respectively, resulting in more glucan. The result with the chs3 mutant is of particular interest, as its nutritional value for Artemia is comparable to the wild type. Hence, only with the chs3 strain, in contrast to the gas1 or mnn9 strains, the temporary protection to VC is not concomitant with a better growth performance under non-challenged conditions, suggesting non-interference of general nutritional effects.