Topostin, a novel inhibitor of mammalian DNA topoisomerase I from Flexibacter topostinus sp. nov. I. Taxonomy, and fermentation of producing strain.

We found a new inhibitor of mammalian DNA topoisomerase I, named topostin, from a bacterial culture. The bacteria was identified as Flexibacter topostinus sp. nov., B-572. Morphological and physiological characteristics, and utilization of sugars were examined. Comparison of the strain with known species of the genus Flexibacter was made and indicates that the strain is a new species of the genus Flexibacter. The bacteria produced the inhibitor in parallel with their growth up to 72 hours.