A novel way to synthesize pantothenate in bacteria involves ß-alanine synthase present in uracil degradation pathway.

Pantothenate is an indispensable vitamin precursor of the synthesis of coenzyme A (CoA), a key metabolite required in over 100 metabolic reactions. ß-Alanine (ß-ala) is an indispensable component of pantothenate. Due to the metabolic relevance of this pathway, we assumed that orthologous genes for ß-alanine synthesis would be present in the genomes of bacteria, archaea, and eukaryotes. However, comparative genomic studies revealed that orthologous gene replacement and loss of synteny occur at high frequency in panD genes. We have previously reported the atypical plasmid-encoded location of the pantothenate pathway genes panC and panB (two copies) in R. etli CFN42. This study also revealed the unexpected absence of a panD gene encoding the aspartate decarboxylase enzyme (ADC), required for the synthesis of ß-ala. The aim of this study was to identify the source of ß-alanine in Rhizobium etli CFN42. In this study, we present a bioinformatic analysis and an experimental validation demonstrating that the source of ß-ala in this R. etli comes from ß-alanine synthase, the last enzyme of the uracil degradation pathway.