Acanthamoeba castellanii as a model for unveiling Campylobacter jejuni host-pathogen dynamics

Fauzy Nasher^*Burhan LehriRichard StablerBrendan Wren^*

• London School of Hygiene and Tropical Medicine, University of London, London, United Kingdom

The persistence of the major enteric pathogen Campylobacter jejuni in the natural environment, despite being microaerophilic, remains unsolved. Its survival in the natural atmospheric environment likely stems from several factors, including interactions with amoebae. C. jejuni transiently interacts with Acanthamoeba and this is thought to provide protection against unfavourable atmospheric conditions and subsequently prime the bacteria for interactions with warm-blooded hosts. Acanthamoeba play vital roles in microbial ecosystems by preying on bacterial species, some of which are clinically important. We analysed the whole transcriptome of A. castellanii infected with C. jejuni 11168H. Our findings provide evidence that infection of A. castellanii with C. jejuni triggers distinct and reproducible cellular responses. Upregulated genes were associated with protein synthesis, DNA damage and repair, gluconeogenic pathways, and protein folding and targeting, while downregulated genes were involved in calcium ion transport, osmotic stress response, energy reserve metabolic processes, and protein hydroxylation. From this data we characterized Cj0979c, named here C. jejuni endonuclease (CjeN), which induces DNA damage in A. castellanii. High-resolution microscopy revealed an unexpected association between C. jejuni and host mitochondria, while infected cells show elevated cytosolic calcium levels and metabolic changes favouring "Warburg-like" metabolism. A. castellanii cells showed increased lactate production, which was subsequently depleted, suggesting that this host metabolic by-product may support C. jejuni survival. These findings identify an unexpected interaction between amoebae and a microaerophilic bacterium and provides a useful model for further research on host-pathogen interactions.This study offers a fresh perspective on understanding the complex interaction between the significant gastrointestinal pathogen Campylobacter jejuni and Acanthamoeba. Leveraging RNA-Seq data, we demonstrate the molecular mechanisms by which C. jejuni manipulates host cellular processes, crucial for its survival. This deeper understanding of bacterial survival and persistence mechanisms in the environment has important implications for public health and environmental microbiology, offering insights into the transmission dynamics of this microaerophilic pathogen.