Sulfate is an important modulator for
virulence factor expression in Bordetella pertussis, the causative organism for
whooping cough. During
infection,
sulfate is released when respiratory epithelial cells are damaged which can affect gene expression. The current predominant strains in Australia are found in single nucleotide polymorphism (SNP) cluster I (ptxP3/prn2). It has been reported that ptxP3 strains have higher
mRNA expression of virulence genes than ptxP1 strains under intermediate
sulfate-modulating conditions (5 mM MgSO4). Our previous proteomic study compared L1423 (cluster I, ptxP3) and L1191 (cluster II, ptxP1) in Thalen-IJssel (THIJS) media without
sulfate modulation and identified an upregulation of
transport proteins and a downregulation of immunogenic
proteins. To determine whether proteomic differences exist between cluster I and cluster II strains in intermediate modulating conditions, this study compared the whole cell
proteome and secretome between L1423 and L1191 grown in THIJS media with 5 mM MgSO4 using iTRAQ and high-resolution multiple reaction monitoring (MRM-hr). Two
proteins (BP0200 and BP1175) in the whole cell were upregulated in L1423 [fold change (FC) >1.2, false discovery rate (FDR) <0.05]. In the secretome, four
proteins from the
type III secretion system (T3SS) effectors were downregulated (FC < 0.8, FDR < 0.05) while six
proteins, including two adhesins,
pertactin (Prn) and tracheal colonization
factor A (TcfA), were upregulated which were consistent with our previous proteomic study. The upregulation of Prn and TcfA in SNP cluster I may result in improved adhesion while the downregulation of the T3SS and other immunogenic
proteins may reduce immune recognition, which may contribute to the increased fitness of cluster I B.
pertussis strains.