Relative activity of the nonphosphorylated B-6 vitamers for Saccharomyces uvarum and Kloeckera brevis in vitamin B-6 microbiological assay.

Accuracy in the microbiological assay of vitamin B-6 is dependent, in part, on equivalent response to each form of the vitamin by the assay organism. Recently, Kloeckera brevis (ATCC 9774) has been suggested as an alternative to Saccharomyces uvarum (ATCC 9080) because of its reported equivalent response to pyridoxine (PN), pyridoxal (PL), and pyridoxamine (PM) in turbidimetric yeast growth assays. Evaluation of the merits of these yeasts in our laboratory yielded contrasting results. As widely reported, S. uvarum exhibited greater growth response with PN than with equivalent molar concentrations of PL or PM. K. brevis exhibited an even greater disparity. Pronounced concentration dependence was observed for the response differences among vitaminers with each organism. On the basis of the variable specificity of K. brevis, this organism is not preferable to S. uvarum for the microbiological determination of total vitamin B-6.