1993 Volume 39 Issue 4 Pages 323-333
Vitamin B12 production by Gram-negative facultative an-aerobic intestinal bacteria, members of the family Enterobacteriaceae, was examined. Klebsiella pneumoniae IFO13541 was the most effective strain with regard to such production. The growth of the strain and its production of vitamin B12 depended exclusively on the concentration of yeast extract added to the medium. The yeast extract components required for the stimulation of bacterial growth and or vitamin B12 production were identified as aspartic acid and pyrroloquinoline quinone (PQQ) and the relationship between vitamin B12 production and these two components was examined. The metabolism of aspartic acid in this process was also investigated; the major metabolites were alanine, glutam-ic acid, and valine. The formation of alanine depended on dehydrogenase, the activity of which was greatly increased with increasing PQQ concen-tration.
