Proteomic comparison of epidemic Australian Bordetella pertussis biofilm cells

Abstract Bordetella pertussis causes whooping cough, a severe respiratory infectious disease. Studies have compared the currently dominant single nucleotide polymorphism (SNP) cluster I (pertussis toxin promoter allele, ptxP3 ) and previously dominant SNP cluster II ( ptxP1 ) strains as planktonic cells. Since biofilm formation is linked with B. pertussis pathogenesis in vivo , this study compared the biofilm formation capabilities of representative strains of cluster I and cluster II. Confocal laser scanning microscopy found that the cluster I strain had a denser biofilm structure compared to the cluster II strain. Differences in protein expression of the biofilm cells were then compared using Tandem Mass Tagging (TMT) and high-resolution multiple reaction monitoring (MRM-hr). In total, 1453 proteins were identified of which 40 proteins had significant differential expression between the two strains in biofilm conditions. Of particular interest was a large increase in expression of energy metabolism proteins (cytochrome proteins PetABC and BP3650) in the cluster I strain. When the expression of these proteins was compared between 6 additional strains from each cluster, it was found that the protein expression varied between all strains. These findings suggest that there are large levels of individual proteomic diversity between B. pertussis strains in biofilm conditions despite the highly conserved genome of the species. Overall, this study revealed visual differences in biofilm structure between B. pertussis strains and highlighted strain specific variation in protein expression that dominate potential cluster specific changes that may be linked with the dominance of cluster I strains. Importance Bordetella pertussis causes whooping cough. The currently circulating cluster I strains have taken over previously dominant cluster II strains. It is important to understand the reasons behind the evolution to develop new strategies against the pathogen. Recent studies have shown that B. pertussis can form biofilms during infection. This study compared the biofilm formation capabilities of a cluster I and a cluster II strain and identified visual differences in the biofilms. The protein expression between these strains grown in biofilms were compared and proteins identified with varied expression were measured with additional strains from each cluster. It was found that despite the highly conserved genetics of the species, there was varied protein expression between the additional strains. This study highlights that strain specific variation in protein expression during biofilm conditions that may dominate the cluster specific changes that may be linked to the dominance of cluster I strains.