Eight 2-deoxystreptamine-negative (DOS^-) mutants were isolated from various strains of Bacillus circulans, normally producing butirosin, xylostasin and ribostamycin. These mutants were classified into two groups (converter and secretor) by the simple method of cosynthesis
using agar plate culture. One of the cosynthetic pairs, strain S-11 and strain 236, was selected for further study From the fermentation broth of strain S-11, an intermediate of DOS biosynthesis, S-11-P, was isolated. This compound was converted to butirosin (BTN) effectively by strain 236. The structure of S-11-P was considered to be (1 L or 1 D)-1, 3, 5/2, 4-5-amino-cyclohexanetetrol, and the pathway of DOS biosynthesis is discussed here.