# A two-step actin-mediated strategy enables Campylobacter jejuni to promote mitochondrial aggregation and iron homeostasis, for intracellular survival and persistence

## TL;DR

Campylobacter jejuni uses a two-step actin strategy to manipulate host mitochondria and iron, helping it survive inside amoebae.

## Contribution

The paper reveals a novel two-phase actin-mediated mechanism involving CiaI and CiaD for intracellular persistence.

## Key findings

- CiaI binds nucleotides and is essential for mitochondrial interaction and localization.
- CiaD promotes actin polymerization and acanthopodia formation for bacterial uptake.
- Iron chelation supports bacterial survival, indicating a role for oxidative stress in host defense.

## Abstract

Campylobacter jejuni, a major cause of bacterial gastroenteritis, is capable of surviving in diverse hosts, including free-living amoebae such as Acanthamoeba. However, the molecular mechanisms that facilitate its intracellular persistence and subsequent transfer remain poorly defined. Here, we hypothesize that C. jejuni employs a biphasic actin-remodelling strategy, mediated by the effector proteins CiaI and CiaD, to reposition and remodel host mitochondria, promoting mitochondrial aggregation and iron homoeostasis. Using dual proteomics, microscopy, biochemical assays, and defined genetic mutants, we show that actin polymerization and CiaI are critical for mitochondrial interaction. We found that CiaI binds nucleotides with cooperative kinetics, acting as a molecular switch, and is crucial for C. jejuni localization near mitochondria, while CiaD promotes actin polymerization and acanthopodia formation to facilitate uptake. We propose a two-phase model: early actin polymerization repositions mitochondria, followed by localized actin depolymerization and mitochondrial remodelling. Iron chelation promotes bacterial survival, suggesting that oxidative stress functions as a host defence. These findings highlight a sophisticated mechanism of intracellular adaptation by C. jejuni that may be relevant to pathogenesis and identify new potential targets for disrupting its environmental and clinical persistence.

Campylobacter jejuni deploys secreted invasion antigens to sequentially remodel host actin, redirecting mitochondria and iron handling in Acanthamoeba castellanii to stabilise an intracellular niche that supports long-term persistence.