Glionitrin A, an antibiotic-antitumor metabolite derived from competitive interaction between abandoned mine microbes

The nutrient conditions present in abandoned coal mine drainages create an extreme environment where defensive and offensive microbial interactions could be critical for survival and fitness. Coculture of a mine drainage-derived Sphingomonas bacterial strain, KMK-001, and a mine drainage-derived Aspergillus fumigatus fungal strain, KMC-901, resulted in isolation of a new diketopiperazine disulfide, glionitrin A (1). Compound 1 was not detected in monoculture broths of KMK-001 or KMC-901. The structure of 1, a (3S,10aS) diketopiperazine disulfide containing a nitro aromatic ring, was based on analysis of MS, NMR, and circular dichroism spectra and confirmed by X-ray crystal data. Glionitrin A displayed significant antibiotic activity against a series of microbes including methicillin-resistant Staphylococcus aureus. An in vitro MTT cytotoxicity assay revealed that 1 had potent submicromolar cytotoxic activity against four human cancer cell lines: HCT-116, A549, AGS, and DU145. The results provide further evidence that microbial coculture can produce novel biologically relevant molecules.

The biological properties of 3,6-epidithiadiketopiperazines. Degradation of gliotoxin-B by Bacillus subtilis (HLX 373)

Like sporidesmin, gliotoxin catalyzes the decomposition of azide in the presence of iodine, and this catalysis can be used for its estimation. The presence of respiring cells of Bacillus subtilis does not interfere with the estimation. Thus it was possible to show that the concentration of gliotoxin decreased when solutions of the antibiotic were incubated with respiring cells. The rate of the decomposition was independent of the gliotoxin concentration in the range 2–25 μg/ml, but was dependent on the number of cells, the pH, and the available nitrogen in the suspending medium. Loss of gliotoxin was most rapid at pH 5.5 and continued when the supernatant was reincubated after centrifugal removal of the cells. No loss of gliotoxin occurred when solutions were incubated in the absence of cells at pH 5.5. By contrast, chemical degradation at pH 8.0 was inhibited in the presence of cells. These results are consistent with the hypothesis that B. subtilis secretes an enzyme which degrades the disulfide group in gliotoxin.