Metabolic shift in the production of corrinoid compounds by Lactobacillus coryniformis in the absence of purines.

Lactobacillus coryniformis CRL 1001 and L. reuteri CRL 1098 have the complete genes necessary to synthesize pseudo-cobalamin as final product in a vitamin B12 free commercial medium. Unlike vitaminB12 (the most biologically active form), the pseudo-cobalamin contains adenine instead of 5,6-dimethlbenzimidazole (DMB) in the Coα-ligand. Considering the vitamin B12-gene clusters of these bacteria, the aim of this work was to analyze the production of corrinoids with DMB (vitamin B12) instead of adenine (pseudo-B12) as lower ligand base in a vitamin B12 free chemically defined medium (CDM) without purines. Genome-wide screening of genes related to purine metabolism showed that both strains possess all pur genes necessary for the synthesis of inositol monophosphate, the main precursor for purine biosynthesis. Accordingly, both strains were able to grow in B12 free CDM without purines, with the supplementation of different synthetic intermediaries. Isolated compounds with positive vitamin B12 activity were quantified and characterized by LC/MS-MS. Total corrinoids values were higher for both strains in comparison to those obtained in vitaminB12 free commercial medium. Interestingly, CRL 1001 strain synthesized cobalamin, suggesting that this strain is able to activate DMB as nitrogenous base instead adenine when it is in excess in a purine-free medium. The present paper represents the first demonstration of a partial metabolic shift to produce vitamin B12 in a Lactobacillus strain.