L-leucine auxotrophy in Bifidobacterium globosum

The enzymes involved in the biosynthetic pathway of L-leucine were studied in plasmid-negative and plasmid-positive clones derived from the RU 809 strain of the Bifidobacterium globosum species. The growth of plasmid-positive clones in synthetic medium required L-leucine. We have shown that no detectable activity of the β-isopropylmalate dehydrogenase enzyme was present in plasmid-positive clones, whereas detectable and significant activity of this enzyme was found in plasmid-negative clones. The lack of activity of the β-isopropylmalate dehydrogenase enzyme is considered responsible for the L-leucine auxotrophy in the plasmid-positive clones.