Malformin A1 as a Mammalian Toxicant from Aspergillus niger

Culture conditions for guanosine production were studied with Bacillus subtilis MG–1 that exclusively accumulated guanosine. Of components investigated, KH₂PO₄, KC1, Fe⁺⁺, Mn⁺⁺, NH₄NO₃ and sodium glutamate have played important roles for guanosine production. The optimal concentrations in the culture medium were 2.0 g, 0.9 g, 7.5 mg, 7.5 mg, 20. 4 g and 6.0 g per liter, respectively.

In particular, the extremely minor concentration of Mn⁺⁺ 0.01 ppm completely repressed guanosine production although the cells grew sufficiently. Amino acids mixture was necessary for cell growth, but not essential for guanosine production.

Under these conditions, MG–1 accumulated 15 g of guanosine per liter in a weight yield of 18.8% of consumed sugar. However, a large amount of acetoin was also found as a byproduct.