Highlights d Knockout of apicoplast TgATS2 disrupts LPA/PA for DrpC recruitment during cytokinesis d T. gondii can sense host environment and adapt to low host nutritional content d Under lipid starvation, parasite FASII and other lipid metabolic genes become essential d Upon nutrient deprivation, T. gondii induces host organelle remodeling and vesiculation

Francisella tularensis, a tier 1 select agent, is the causative bacterium of tularemia, a zoonosis with a large animal reservoir. However, F. tularensis, like many other Francisella species (including F. novicida and F. philomiragia), is assumed to have an aquatic reservoir. The mechanisms of Francisella species persistence in surface water remain poorly characterized. In this study, we deeply investigated the long-term interactions of the tularemia agent F. tularensis subsp. holarctica, F. novicida or F. philomiragia with amoebae of the Acanthamoeba species. In amoeba plate screening tests, all the Francisella species tested resisted the attack by amoebae. In in vitro infection models, intra-amoebic growth of Francisella varied according to the involved bacterial species and strains, but also the amoeba culture medium used. In co-culture models, the amoebae favoured Francisella survival over 16 days. Such enhanced survival was likely dependent on direct contact between bacteria and amoebae for F. novicida and on amoeba-excreted compounds for F. novicida and for F. tularensis. In a spring water co-culture model, amoebae again enhanced F. novicida survival and preserved bacterial morphology. Overall, our results demonstrate that amoebae likely promote Francisella survival in aquatic environments, including the tularemia agent F. tularensis. However, bacteria-amoebae interactions are complex and depend on the Francisella species considered.