The inclusion of a transgenic probiotic expressing recombinant phytase in a diet with a high content of vegetable matter markedly improves growth performance and the expression of growth-related genes and other selected genes in zebrafish

Aquaculture is an important sector of world food production for which the source of protein for commercial diets is a huge bottleneck. Vegetable proteins are cheaper, but are accompanied by antinutritional compounds like phytate. Phytases are enzymes produced in microorganisms capable of degrading phytate. The addition of purified phytases to commercial feed improves the nutrient bioavailability of vegetable matter. However, the production and purification of phytases has a high cost. An alternative is to genetically manipulate a probiotic bacterium to produce and secrete phytase directly into the host's digestive tract. In the present study, a strain of Bacillus subtilis was engineered to produce and secrete a fungal phytase. The fish fed with a high vegetable content supplemented with transgenic probiotic showed an improvement in the parameters analysed. These results were corroborated with the expression of genes related to peptide transport (s1c15a1b and slc15a2), appetite (ghrl), somatic growth (igf1, myod and myog) and bone metabolism (bglap). All the analysed genes were strongly induced in the group of fish treated with the transgenic probiotic, corroborating with the results observed for the parameters. This study shows, for the first time, that a transgenic probiotic expressing recombinant phytase is able to minimize the antinutritional effects of the high content of vegetal matter included in the fish diet. The results presented herein open the possibility of transgenic probiotics being used as bioreactors for the production of molecules capable of interfering in other physiological systems in fish.