Amoebae Can Promote the Survival of Species in the Aquatic Environment

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