Role of DsbG in acid tolerance and flagella-mediated motility of Listeria monocytogenes

Abstract:

[Objective] To investigate the biological roles of the disulfide bond formation protein DsbG in the acid tolerance and flagella-mediated motility of Listeria monocytogenes by constructing the dsbG-deleted and complemented strains. [Methods] The dsbG-deleted and complemented strains were constructed via the homologous recombination method. The growth and survival rates of the strains in the media at different pH gradients were analyzed. The transcriptional levels of the genes involved in acid tolerance were determined by real-time quantitative PCR and compared between the wild-type and mutant strains exposed to acid stress. The motility, transcriptional levels of flagella-associated genes, and flagellar morphology were compared between wild-type and mutant strains by semi-solid culture, real-time quantitative PCR, and transmission electron microscopy, respectively. [Results] The deletion of dsbG did not affect the growth of the bacteria in a medium with neutral pH. However, it significantly reduced the survival rate of bacteria in the media with hydrochloric acid and citric acid (pH 3.5). It down-regulated the transcriptional levels of the genes (argD and argF) in the arginine pathway by 2.4 and 3.7 times, respectively. Moreover, the lack of dsbG impaired the flagellum formation and bacterial motility and down-regulated the transcriptional levels of flagella-associated genes flaA, flgB, and flgD by 29.7, 6.7, and 6.9 times, respectively, compared with the wild-type strain. [Conclusion] This study for the first time, demonstrated that DsbG could sense low pH stress, play a role in the development of acid tolerance, and more importantly, contribute to the flagella-mediated motility of L. monocytogenes via regulating the transcription of flagella-associated genes. This study helps to understand the roles of the disulfide bond formation protein family in the environmental adaptation of L. monocytogenes and provides a theoretical basis for the prevention and control of foodborne pathogens.

Key words:Listeria monocytogenes;disulfide bond formation protein;acid tolerance;motility;flagella