Investigating iron uptake systems in C. jejuni and C. coli

Campylobacter species are Gram-negative, microaerophilic bacterial colonisers of farmed animals and are the leading cause of human gastroenteritis. Iron is a crucial metabolite and co-factor for many processes that facilitate host gut colonisation and over-coming the non-specific host defence mechanism of iron restriction is key. Campylobacter species therefore possess multiple iron uptake systems to enable the utilisation of iron in various complexes.

The haem uptake system (chuABCDZ), Fe2+ uptake system (feoB/cj1937), and rhodotorulic acid uptake system (p19/cj1658) were found to be 100% conserved in large database of C. jejuni and C. coli isolates, demonstrating these are key systems for the bacteria. Species, source, and clonal complex of the isolates all showed an association with iron uptake system distribution. ST-21 complex isolates were found to be more likely to possess all iron uptake systems, with ST-45 complex isolates significantly less likely to. C. coli isolates were significantly more likely to possess a functional CfrB enterochelin uptake system and isolates associated with human sources were significantly more likely to possess the CfrA enterochelin uptake system and the CtuA transferrin uptake system.

Mutation of the C. jejuni chuA gene resulted in an increased survival with human macrophages and the ST-45 clonal complex isolate M1 mutant also showed increased adhesion, invasion, and survival in human and avian intestinal epithelial cells. This indicates the possession of the ChuA system is detrimental to invasion and intracellular survival despite its conservation, with the impact of chuA mutation higher in macrophages. The impact of chuA deletion in M1 was more significant than in ST-21 clonal complex isolate NCTC 11168, indicating the extent of the effect of chuA mutation may be influenced by other iron uptake systems present.

GAPDH was confirmed to be present in the C. jejuni membrane so its physical location allows the possibility of ferri-lactoferrin interaction. However, gapA mutation was unsuccessful as multiple C. jejuni laboratory strains appeared to show a metabolic conflict with the possession of a functioning Entner-Doudoroff pathway, resulting in no bypass of GAPDH’s metabolic role. However, the metabolic conflict elucidated by this attempt merits further investigation.