Biosynthesis of thiamin. Different biosynthetic routes of the thiazole moiety of thiamin in aerobic organisms and anaerobic organisms.

The nitrogen atom of glycine was incorporated into the thiazole moiety of thiamin in the aerobic microorganisms Bacillus subtilis, Pseudomonas putida, Saccharomyces cerevisiae, Mucor racemosus, Neurospora crassa, and Emericella nidulans. It was not incorporated in the case of the facultative anaerobic microorganisms Escherichia coli and Enterobacter aerogenes, which, however, did incorporate the nitrogen atom of tyrosine. These results show that aerobic microorganisms and facultative anaerobic microorganisms have different biosynthetic pathways for the thiazole moiety of thiamin.