Bordetella pertussis uses a
type III secretion system (T3SS) to inject virulence
proteins into host cells. Although the B.
pertussis T3SS was presumed to be involved in host colonization, efficient secretion of type III secreted
proteins from B.
pertussis has not been observed. To investigate the roles of type III secreted
proteins during
infection, we attempted to optimize culture conditions for the production and secretion of a type III secreted
protein, BteA, in B.
pertussis We observed that B.
pertussis efficiently secretes BteA in
ascorbic acid-depleted (AsA-) medium. When L2 cells, a rat lung epithelial cell line, were infected with B.
pertussis cultured in the AsA- medium, BteA-dependent cytotoxicity was observed. We also performed an immunofluorescence assay of L2 cells infected with B.
pertussis Clear fluorescence signals of Bsp22, a needle structure of T3SS, were detected on the bacterial surface of B.
pertussis cultured in the AsA- medium. Since
ascorbic acid is known as a
reducing agent, we cultured B.
pertussis in liquid medium containing other
reducing agents such as
2-mercaptoethanol and
dithioerythritol. Under these reducing conditions, the production of type III secreted
proteins was repressed. These results suggest that in B.
pertussis, the production and secretion of type III secreted
proteins are downregulated under reducing conditions.IMPORTANCE The
type III secretion system (T3SS) of Bordetella pertussis forms a needlelike structure that protrudes from the bacterial cell surface. B.
pertussis uses a T3SS to translocate virulence
proteins called effectors into host cells. The culture conditions for effector production in B.
pertussis have not been investigated. We attempted to optimize culture medium compositions for producing and secreting type III secreted
proteins. We found that B.
pertussis secretes type III secreted
proteins in
reducing agent-deprived liquid medium and that BteA-secreting B.
pertussis provokes cytotoxicity against cultured mammalian cells. These results suggest that redox signaling is involved in the regulation of B.
pertussis T3SS.