Growth Response of the Yeasts Saccharomyces uvarum and Kloeckera brevis to the Free Biologically Active Forms of Vitamin B-6

The ideal microorganism for the microbiological assay of total vitamin B-6 should respond equally to all forms of vitamin B-6. The yeasts Saccharomyces uvarum (ATCC 9080) and Kloeckera brevis (ATCC 9774) were compared in their ability to utilize pyridoxine, pyridoxal and pyridoxamine in the concentration range needed for the measurement of vitamin B-6 in biological materials. Our results showed that K. brevis responded equally to all three free forms of vitamin B-6 at a dosage range of 2–10 ng molar equivalent of pyridoxine. In contrast, S. uvarum, which is currently widely used for the vitamin B-6 assay, had a significantly different growth response to three forms of vitamin B-6 at the comparable dosage range. The results suggest that the yeast K. brevis is better suited for the microbiological assay of total vitamin B-6.