Influence of Niacin on the Growth-stimulating Effect of Inositol on Saccharomyces carlsbergensis

Abstract

IN preliminary investigations to establish the most suitable method for the estimation of inositol, we also tried the method described by Atkin et al.¹ utilizing Saccharomyces carlsbergensis (A.T.C.C. 9080). Their method utilizes a medium without niacin. Hopkins and Pennington² and Rabinowitz and Snell³ have pointed out that the addition of niacin to the medium for the determination of vitamin B₆ by the same test organism prevented accidental high assay values. As our samples would contain appreciable amounts of niacin, we found it of importance to establish if niacin had any effect on the growth response in the inositol assay of Atkin et al.¹. We found a marked depression of the growth-stimulating effect of inositol when niacin was added to the medium (Fig. 1). In order to establish the relation of this growth-depressing effect, experiments were carried out by adding graded amounts of niacin to tubes containing sub-optimal inositol contents (1.5 µg/tube). The assays were carried out with a total volume of 5 ml. and incubation for 18 h at 30° C in a shaking incubator. The growth-depressing effect increased with increased niacin concentration up to about 10 µg/tube (Fig. 2).