1. Suitable agar plate media were selected for isolation of nucleotide producing strains, by salvage synthesis, from natural sources. Since this agar medium contains a high con-centration of phosphates, manganese and glucose, it is specific for these bacteria.
2. With this plate medium, 113 bacterial strains accumulating 5'inosinic acid (IMP) or IMP-like substances were isolated effectively from feces of a variety of birds and mammals and from soils.
Some of the strains isolated were recognized to accumulate other nucleotides, purine bases and sugars, such as guanine nucleotides, XMP, xanthine, ribulose or xylnlose, with or without hypoxanthine in the media.
3. Five strains of IMP accumulating bacteria were identified; two were classified as Brevibacterium, two as Corynebacterium and one as Arthrobacterium species by taxonomical studies. But their characteristics did not completely coincide with those of bacteria described in Bergey's manual.
4. One of the IMP producing bacteria isolated, culture No. 21-26, actually consisted of two separate strains, namely No. 21-26-101 and No. 21-26-102. The highest production of IMP or guanine nucleotides was obtained, when each strain was inoculated together to the fermentation medium from each seed culture in the same inoculum size.
5. The nucleotide productions by No. 21-26-101 or No. 21-26-102 with authentic strains were examined by the mixed culture technique. It was found that production of IMP or guanine nucleotides by Brevibacterium ammoniagenes ATCC 6871 was stimulated remarkably in the presence of No. 21-26-102.