Producción de Vitamina B12 por Lactobacilos: estudios moleculares y funcionales

Tesis

Resumen

Vitamin B12 or cobalamin is an essential metabolite in humans because it participates in two fundamental cellular reactions, the synthesis of methionine from homocysteine (DNA synthesis) and the conversion of methylmalonyl-CoA in succinyl-CoA (propionyl-CoA utilization to obtaining ATP). Cobalamin is exclusively synthesized by some bacterial and archaea strains. Although some vitamin-producing bacteria are found in the rumen of cattle, sheep and goats, they are not in the intestinal microbiota of human and other animals. For this reason, humans must incorporate cobalamin from foods of animal origin or pharmaceutical products. In this context, the strict vegetarian diets and/or malnutrition can cause a vitamin B12 deficiency, and this could be intensified in case of pregnancy, lactation, old age and childhood. The Lactobacillus genus is presented, within the group of Lactic Acid Bacteria, as a nutraceuticals producer due to the ability to synthesize essential metabolites such as vitamin B12. In this Doctoral Thesis, we studied two Lactobacillus strains vitamin B12 producers at genomic and biochemical levels to characterize the production routes of each strain and determine the optimal production conditions of this macromolecule. In addition, we carried out in silico studies of genomes deposited in the database searching genes that encode proteins necessary for the vitamin B12 biosynthesis in other Lactobacillus strains isolated from different ecological niches. Finally, the bioavailability of the produced metabolite in a food substrate of vegetable origin, as the soybean aqueous extract, was proved by an experimental mice model of nutritional vitamin deficiency. In this thesis work, for the first time it was demonstrated that Lactobacillus reuteri CRL 1098 and Lactobacillus coryniformis CRL 1001 have specific genetic differences that lead to different biosynthetic pathways, being the most commonly known route found in the CRL 1001 strain. The biochemical studies showed a higher vitamin production of both strains with the addition of intermediaries, as cobalt and 5,6- dimethylbenzimidazole, to the culture medium. However, the addition of L-threonine to the culture medium improved only the CRL 1001 vitamin production. In vivo studies showed that the CRL 1001 strain grown in soybean aqueous extract was able to revert the vitamin B12 deficiency diet in female mice and their progeny. The studies carried out in this doctoral thesis established the biochemical, physiological and functional bases of vitamin B12 production by lactic acid bacteria strains to develop in the future stage an applied research aimed to obtain a successful technological product.

Descargue o solicite el texto completo:

http://hdl.handle.net/11336/88452