Yeast Nitrogen Base without Amino Acids is formulated as per Wickerham (1, 2) and is used for investigating amino acid and carbohydrate requirement of yeasts. This medium has the same composition as Yeast Nitrogen Base (M139) medium except the amino acids histidine, methionine and tryptophan.
Inoculate media tubes with very light inoculum and incubate at 25°C for 6-7 days and again for 20-24 days. Draw lines with India ink on a paper. If lines are not seen or appear diffused through the culture, the test is considered positive and if the lines are distinguishable, test is considered negative.
Directions: For best results the medium is prepared in 10X strength. Suspend 6.7 grams in 100 ml distilled water. Add 5 grams dextrose or an equivalent amount of other carbohydrate and other chemicals like amino acids that modify growth of yeasts as desired. Ensure complete solution and sterilize by filtration. For use, dilute 0.5 ml 10X medium to make 5 ml with sterile distilled water. Mix well.