Differential roles of catalase-encoding genes (katA and katB) in response to oxidative stress and antibiotics in Pseudomonas aeruginosa

Abstract

Bacterial cells growing under aerobic conditions produce reactive oxygen species that damage macromolecules, which leads to cellular death. However, bacterial cells possess oxidative stress-scavenging systems that detoxify these reactive oxygen species. Antibiotics can induce oxidative stress, which contributes to cellular death alongside their specific killing mechanisms. An imbalance between the oxidative stress-scavenging systems and antibiotic-induced oxidative stress may affect bacterial survival or death. Catalases are one of the oxidative stress-scavenging systems and detoxify hydrogen peroxide, thereby protecting cells from oxidative stress. Pseudomonas aeruginosa is a Gram-negative human pathogen and has multiple genes encoding catalase. This study explores the roles of catalase-encoding genes (katA and katB) in response to oxidative stress and antibiotics in P. aeruginosa. The catalase-encoding genes were knocked out in P. aeruginosa PAO1 and clinical isolates. The resulting mutant strains (katA::Tc, katB::Gm, katA::Tc/katB::Gm) were tested for their susceptibility to hydrogen peroxide, superoxide, and antibiotics. The results showed that the katA::Tc was more susceptible to hydrogen peroxide, while the katB::Gm was more susceptible to superoxide. MIC (minimum inhibitory concentration) levels for katB::Gm with chloramphenicol were decreased by 2- to 4-fold compared to the parental strain. However, MIC levels for katA::Tc remained unchanged for all antibiotics tested. These results indicate that katA and katB detoxify both hydrogen peroxide and superoxide, with katA being more effective against hydrogen peroxide and katB being more effective against superoxide than vice versa. Furthermore, katB appears to confer resistance to oxidative stress induced by chloramphenicol in P. aeruginosa.