Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2012
Publication Date: 10/24/2012
Citation: Hester, S.E., Lui, M., Nicholson, T., Nowacki, D., Harvil, E.T. 2012. Identification of a CO2 responsive regulon in Bordetella. PLoS One. 7(10):e47635. Interpretive Summary: Many bacterial pathogens have developed sophisticated mechanisms that enable them to sense and respond to different microenvironments within or outside of a host. Here we show that Bordetella species, a common respiratory pathogen in many host species, regulate the production of virulence factors and other antigens in response to carbon dioxide levels that mimic conditions within a diseased host. We found many strains of Bordetella bronchiseptica produce an increased amount of virulence factors in response to increased CO2 conditions that may occur in the respiratory tract during disease such as viral pneumonia. The human pathogens B. pertussis and B. parapertussis also increase production of several virulence factors when grown in conditions mimicking CO2 levels in a diseased lung, indicating that this response is conserved among this family of bacteria. Together, our data demonstrate that Bordetella species can sense and respond to physiologically relevant changes in CO2 concentrations that mimic disease conditions in the lung. This new data provides insight as to how production of various bacterial virulence factors is triggered and explains a mechanism by which this family of pathogens can take advantage of a sick host and cause severe secondary bacterial disease. Targeting this sensing mechanism for future vaccines may provide a new and improved method to prevent secondary bacterial infections in many species.
Technical Abstract: Sensing the environment allows pathogenic bacteria to coordinately regulate gene expression to maximize survival within or outside of a host. Here we show that Bordetella species regulate virulence factor expression in response to carbon dioxide levels that mimic in vivo conditions. We found strains of Bordetella bronchiseptica that did not produce adenylate cyclase toxin (ACT) when grown in liquid or solid media with ambient air aeration, but produced ACT and additional antigens when grown in air supplemented to 5% CO2. Transcriptome analysis and quantitative real time-PCR analysis revealed that strain 761, as well as strain RB50, increased transcription of genes encoding ACT, filamentous hemagglutinin (FHA), pertactin, fimbriae and the type III secretion system in 5% CO2 conditions, relative to ambient air. Furthermore, transcription of cyaA and fhaB in response to 5% CO2 was increased in the absence of BvgS. In vitro analysis also revealed increases in cytotoxicity and adherence when strains were grown in 5% CO2. The human pathogens B. pertussis and B. parapertussis also increased transcription of several virulence factors when grown in 5% CO2, indicating that this response is conserved among the classical bordetellae. Together, our data indicate that Bordetella species can sense and respond to physiologically relevant changes in CO2 concentrations by regulating virulence factors important for colonization, persistence and evasion of the host immune response.