Polyphosphate kinase 1 is a pathogenesis determinant in Campylobacter jejuni

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in the developed world. Despite its prevalence, relatively little is known about C. jejuni's precise pathogenesis mechanisms, particularly in comparison to other well-studied enteric organisms such as Escherichia coli and Salmonella spp. Altered expression of phosphate genes in a C. jejuni stringent response mutant, together with known correlations between the stringent response, polyphosphate (poly-P), and virulence in other bacteria, led us to investigate the role of poly-P in C. jejuni stress survival and pathogenesis. All sequenced C. jejuni strains harbor a conserved putative polyphosphate kinase I predicted to be principally responsible for poly-P synthesis. We generated a targeted ppk1 deletion mutant (Delta ppk1) in C. jejuni strain 81-176 and found that Delta ppk1, as well as the Delta spoT stringent response mutant, exhibited low levels of poly-P at all growth stages. In contrast, wild-type C. jejuni poly-P levels increased significantly as the bacteria transitioned from log to stationary phase. Phenotypic analyses revealed that the Delta ppk1 mutant was defective for survival during osmotic shock and low-nutrient stress. However, certain phenotypes associated with ppk1 deletion in other bacteria (i.e., motility and oxidative stress) were unaffected in the C. jejuni Delta ppk1 mutant, which also displayed an unexpected increase in biofilm formation. The C. jejuni Delta ppk1 mutant was also defective for the virulence-associated phenotype of intraepithelial cell survival in a tissue culture infection model and exhibited a striking, dose-dependent chick colonization defect. These results indicate that poly-P utilization and accumulation contribute significantly to C. jejuni pathogenesis and affect its ability to adapt to specific stresses and stringencies. Furthermore, our study demonstrates that poly-P likely plays both similar and unique roles in C. jejuni compared to its roles in other bacteria and that poly-P metabolism is linked to stringent response mechanisms in C. jejuni.