Conventional and unconventional probiotics in the experimental culture of white shrimp Litopenaeus vannamei
Probiotics exert numerous beneficial effects in aquaculture, especially with regard to zootechnical performance, feed conversion and immune response. Several microorganisms can be characterized as probiotics and the development of biotechnology has allowed these microorganisms to be used as platforms for the expression of heterologous proteins, which can enhance the already recognized beneficial effects of conventional probiotics. In this Thesis, three experiments of 45 days were carried out, each one testing a different probiotic as an additive in the diet of the shrimp Litopenaeus vannamei. In chapter I, the probiotic potential of a strain of Bacillus subtilis (strain E) previously isolated from the gastrointestinal tract of shrimp was tested. In this study, parameters such as zootechnical performance, centesimal composition of muscle tissue, number of lipid vacuoles in the hepatopancreas and the expression of genes related to digestion, amino acid metabolism and antioxidant defenses were evaluated. The results showed that the supplementation of the diet with the E strain did not affect the zootechnical performance of the shrimp, but increased the concentration of lipids in the muscle and in the hepatopancreas. In addition, genes related to digestive processes and amino acid metabolism were strongly reduced, indicating that dietary supplementation with the E strain of B. subtilis can improve the absorption of nutrients from the feed and minimize the toxic effects of nitrogenous compounds present in drinking water. cultivation. In chapter II, the objective was to evaluate the effect of a genetically modified strain of B. subtilis KM0 that expresses and secretes a fungal phytase, which can improve nutritional aspects related to phosphorus metabolism in shrimp. When added to the commercial feed of L. vannamei, this genetically modified B. subtilis did not significantly alter growth parameters. However, there was a decrease in the expression of genes related to digestion and an increase of 39% in the phosphorus content in the muscle tissue, and also an increase in the count of lipid vacuoles in the shrimp hepatopancreas. In chapter III, the objective was to supplement the commercial feed with a genetically modified strain of the cyanobacterium Synechococcus elongatus expressing a heterologous β-glucosidase, which can impact carbohydrate metabolism in shrimp. The results showed that the supplementation of the commercial feed with cyanobacteria (wild or transgenic) did not negatively affect the growth rates, final weight and feed conversion ratio of the shrimp compared to the controls. However, the cyanobacteria altered the expression of genes related to digestion (amy, gdh and cathB) and the immune system (tgase), while the transgenic cyanobacteria, alone, significantly increased the phosphorus and lipid content in the shrimp muscle. In conclusion, this thesis demonstrated that the use of probiotics isolated from the intestinal tract of shrimp L. vannamei as well as genetically modified probiotics can bring several benefits to shrimp, which is interesting from an environmental and economic point of view, contributing to sustainability. of carcinoculture.