A Microbiological Assay Method for Biotin

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Abstract
The test organism, a strain of Allescheria boydii, (no. 1699 of the authors'' culture collection) was a natural mutant which had lost its capacity to synthesize biotin. Five ml. of double concentration of a basal medium (containing dextrose, asparagine, buffer and minerals) plus l-5ml. of biotin standard soln. or the extract to be tested were autoclaved for 15 min. at 120[degree]C. The spore suspension for inoculum was prepared by adding 10 ml. of the basal medium to a culture and scraping the surface of the culture with a platinum loop. A drop of suspension was inoculated into the medium of each flask. Incubation was carried out at room temp. for 8 days. The samples were then autoclaved, the pads removed, washed, pressed out on filter paper, rolled into pellets, dried at 110[degree]C for 2 hrs. and weighed. The standard curve was determined by the addition of 1, 5, 10, 50 and 100m[mu]g. of biotin per flask. The reliability of the method was indicated by the reproducibility of assays and good re-coveries when biotin was added to rat liver, yeast extract and purified casein.