A Rapid in Vivo Colorimetric Library Screen for Inhibitors of Microbial Respiration

A number of fungicides that target the respiratory chain enzymes complexes II and III are used in agriculture. They are active against a large range of phytopathogens. Unfortunately, the evolution of fungicide resistance has quickly become a major issue. Resistance is often caused by mutations in the inhibitor binding domains of the complexes, and new molecules are required that are able to bypass such resistance mutations. We report here on a rapid in vivo high-throughput method, using yeast and the redox dye TTC to screen chemical libraries and identify inhibitors of respiratory function. We applied that screening process, followed by a series of tests, to a diverse library of 4,640 molecules and identified a weak inhibitor of complex III without toxic effect on the cell. Interestingly, that drug (D12) is fully active against the mutant enzyme harboring the G143A mutation that confers a high level of resistance toward most of the fungicides targeting complex III but is not active against bovine complex ...