Exploring the antibacterial action of gliotoxin: Does it induce oxidative stress or protein damage?

The study aimed to investigate the effects of gliotoxin (GTX), a secondary fungal metabolite belonging to the epipolythiodioxopiperazines class, on Gram-positive and Gram-negative bacteria. While the cytotoxic mechanism of GTX on eukaryotes is well understood, its interaction with bacteria is not yet fully comprehended. The study discovered that S. epidermidis displayed a higher uptake rate of GTX than E.coli. However, Gram-negative bacteria required higher doses of GTX than Gram-positive bacteria to experience the bactericidal effect, which occurred within 4 h for both types of bacteria. The treatment of bioluminescent sensor E.coli MG1655 pKatG-lux with GTX resulted in oxidative stress. Pre-incubation with the antioxidant Trolox did not increase the GTX inhibitory dose, however, slightly increased the bacterial growth rate comparing to GTX alone. At the same time, we found that GTX inhibitory dose was significantly increased by the pretreatment of bacteria with 2-mercaptoethanol and reduced glutathione. Using another biosensor, E. coli MG1655 pIpbA-lux, we showed that bacteria treated with GTX exhibited heat shock stress. SDS-page electrophoresis demonstrated protein aggregation under the GTX treatment. In addition, we have found that gliotoxin's action on bacteria was significantly inhibited when zinc salt was added to the growth medium.