Identification and characterization of BipA, a Bordetella Bvg‐intermediate phase protein

Abstract

The Bordetella BvgAS sensory transduction system has traditionally been viewed as controlling a transition between two distinct phenotypic phases: the Bvg+ or virulent phase and the Bvg− or avirulent phase. Recently, we identified a phenotypic phase of Bordetella bronchiseptica that displays reduced virulence in a rat model of respiratory infection concomitant with increased ability to survive nutrient deprivation. Characterization of this phase, designated Bvg‐intermediate (Bvgi), indicated the presence of antigens that are maximally, if not exclusively, expressed in this phase and therefore suggested the existence of a previously unidentified class of Bvg‐regulated genes. We now report the identification and characterization of a Bvgi phase protein, BipA (Bvg‐intermediate phase protein A), and its structural gene, bipA. Reverse transcriptase–polymerase chain reaction (RT–PCR) analysis indicates that bipA is expressed maximally under Bvgi phase conditions and thus represents the first identified Bvgi phase gene. bipA encodes a 1578‐amino‐acid protein that shares amino acid sequence similarity at its N‐terminus with the proposed outer membrane localization domains of intimin (Int) of enteropathogenic and enterohaemorrhagic Escherichia coli and invasin (Inv) of Yersinia spp. Although not apparent at the amino acid level, BipA is also similar to Int and Inv in that the proposed membrane‐spanning domain is followed by several 90‐amino‐acid repeats and a distinct C‐terminal domain. Localization studies using an antibody directed against the C‐terminus of BipA indicated that its C‐terminus is exposed on the bacterial cell surface. Western blot analysis with this same antibody indicated that BipA homologues are expressed in Bvgi phase Bordetella pertussis and Bordetella parapertussis. Comparison of a ΔbipA strain with wild‐type B. bronchiseptica indicated that BipA is not required for Bvgi phase‐specific aggregative adherence to rat lung epithelial cells in vitro or for persistent colonization of the rabbit respiratory tract in vivo. However, our data are consistent with the hypothesis that BipA, and the Bvgi phase in general, play an important role in the Bordetella infectious cycle, perhaps by contributing to aerosol transmission.

Novel, host-restricted genotypes of Bordetella bronchiseptica associated with phocine respiratory tract isolates

“…The virulence gene found to be most divergent in seal isolates as compared with other closely related isolates is bipA. The function of BipA is unknown, but it is postulated to be an adhesin on the basis of sequence similarity with the bacterial adhesins intimin and invasin (Stockbauer et al, 2001). A study comparing bipA genes of B. bronchiseptica isolates from several different hosts, including the rabbit isolate RB50, found all isolates have the same allele, with eight 90 aa repeats and no nucleotide substitutions over the remaining 39 end of the gene (Fuchslocher et al, 2003).…”

“…During growth at~26 u C or below, or in the presence of millimolar concentrations of MgSO 4 (Cotter & Miller, 1997). The Bvg i phase is characterized by expression of a subset of Bvg + genes in addition to Bvg i -specific genes such as bipA, a surface-exposed protein with similarity to intimin in Escherichia coli and invasin of Yersinia species (Stockbauer et al, 2001).…”

Proteome approaches combined with Fourier transform infrared spectroscopy revealed a distinctive biofilm physiology in Bordetella pertussis

“…For example the autotransporter pertactin, other putative adhesins such as BipA and the prominent outer membrane porin protein BP0840 [44][45][46] were significantly upregulated in biofilm. For a number of microorganisms the expression of surface proteins, like BapA in Staphylococcus aureus and Ag43 in Escherichia coli [47,48], has been reported to be essential for proper biofilm formation.…”

Signal Transduction by BvgS Sensor Kinase

“…In addition to the Bvg Ϫ and Bvg ϩ phases, B. pertussis can be in an intermediate phase, in which a subset of virulence factors are expressed together with specific intermediate genes (5,(7)(8)(9). In vitro, intermediate levels of activity occur at intermediate concentrations of nicotinate.…”

“…This sets the bacte-ria in the avirulent, Bvg Ϫ phase. An intermediate phase occurs at moderate modulator concentrations, in which only the "early" virulence genes are transcribed together with intermediate genes (5,(7)(8)(9). The different phases of B. pertussis might correspond to distinct stages in the development of the infectious cycle.…”