Role of yceA-cybB-yceB operon in oxidative stress tolerance, swimming motility and antibiotic susceptibility of Stenotrophomonas maltophilia

Background: Stenotrophomonas maltophilia is ubiquitous in the environment and is an important MDR opportunistic pathogen. Oxidative stress is an inevitable challenge to an aerobic bacterium. Accordingly, S. maltophilia has many capabilities to face variable oxidative stress. Some of the oxidative stress alleviation systems cross-protect bacteria from antibiotics. In our recent RNA-sequencing transcriptome analysis, we documented the increased expression of a three-gene cluster, yceA-cybB-yceB, in the presence of hydrogen peroxide (H₂O₂). The YceI-like, cytochrome b561 and YceI-like proteins encoded by yceA, cybB and yceB are located in the cytoplasm, inner membrane and periplasm, respectively. Objectives: To characterize the role of the yceA-cybB-yceB operon of S. maltophilia in oxidative stress tolerance, swimming motility and antibiotic susceptibility. Methods: The presence of the yceA-cybB-yceB operon was verified by RT-PCR. The functions of this operon were revealed by in-frame deletion mutant construction and complementation assay. Expression of the yceA-cybB-yceB operon was assessed by quantitative RT-PCR. Results: The yceA, cybB and yceB genes form an operon. Loss of function of the yceA-cybB-yceB operon compromised menadione tolerance, enhanced swimming motility and increased susceptibility to fluoroquinolone and β-lactam antibiotics. The expression of the yceA-cybB-yceB operon was up-regulated by oxidative stress, such as H₂O₂ and superoxide, and not impacted by antibiotics, such as fluoroquinolone and β-lactams. Conclusions: The evidence strongly supports the view that the physiological function of the yceA-cybB-yceB operon is to alleviate oxidative stress. The operon provides an additional example that oxidative stress alleviation systems can cross-protect S. maltophilia from antibiotics.