Bacterial DNA gyrase is an essential type II topoisomerase that enables cells to overcome topological barriers encountered during replication, transcription, recombination, and repair. This enzyme is ubiquitous in bacteria and represents an important clinical target for antibacterial therapy. In this paper we report the characterization of three exciting new gyramide analogs—from a library of 183 derivatives—that are potent inhibitors of DNA gyrase and are active against clinical strains of gram-negative bacteria (Escherichia coli, Shigella flexneri, and Salmonella enterica; 3 of 10 wild-type strains tested) and gram-positive bacteria (Bacillus spp., Enterococcus spp., Staphylococcus spp., and Streptococcus spp.; all 9 of the wild-type strains tested). E. coli strains resistant to the DNA gyrase inhibitors ciprofloxacin and novobiocin display very little cross-resistance to these new gyramides. In vitro studies demonstrate that the new analogs are potent inhibitors of the DNA supercoiling activity of DNA gyrase (IC50s of 47–170 nM) but do not alter the enzyme’s ATPase activity. Although mutations that confer bacterial cells resistant to these new gyramides map to the genes encoding the subunits of the DNA gyrase (gyrA and gyrB genes), overexpression of GyrA, GyrB, or GyrA and GyrB together does not suppress the inhibitory effect of the gyramides. These observations support the hypothesis that the gyramides inhibit DNA gyrase using a mechanism that is unique from other known inhibitors.

Bacterial cell division requires identification of the division site, assembly of the division machinery, and constriction of the cell envelope. These processes are regulated in response to several cellular and environmental signals. Here, we use small molecule iron chelators to characterize the surprising connections between bacterial iron homeostasis and cell division. We demonstrate that iron starvation downregulates the transcription of genes encoding proteins involved in cell division, reduces protein biosynthesis, and prevents correct positioning of the division machinery at the division site. These combined events arrest the constriction of the cell during late stages of cytokinesis in a manner distinct from known mechanisms of inhibiting cell division. Overexpression of genes encoding cell division proteins or iron transporters partially suppresses the biological activity of iron chelators and restores growth and division. We propose a model demonstrating the effect of iron availability on the regulatory mechanisms coordinating division in response to the nutritional state of the cell.