Deciphering the ecology and functioning of the symbiotic relationships between nanobacteria (CPR) and magnetotactic bacteria – MTB-CPR

Metagenomics has revealed a tremendous number of uncultivated bacterial clades referred as the ‘microbial dark matter’, including a large group of nano-sized bacteria forming the candidate phyla radiation (CPR) accounting >15% of bacterial diversity. CPR are mainly composed of symbiotic organisms with key roles in ecosystem formation and nutrient cycling. In recent years, several studies have described the ecology, diversity and functioning of some CPR bacteria classified as predatory bacteria, but observations are not easy, remain random and only few hosts have been identified. Recently, our consortium reproducibly observed and identified different magnetotactic bacteria (MTB) populations inhabiting microoxic-anoxic habitats hosting nano-sized CPR bacteria. CPR cells are associated partially inside its magnetotactic host, which seems to modify its external membrane in response to the CPR contact. Thus, our observations rather suggest that MTB-CPR symbioses last over time without host disintegration and could also rely on a mutualistic interaction. The magnetism of MTB represents an advantage to characterize the functional bases of the interaction. In this project, we will tackle low risk/high gain reachable challenges with the study of the biodiversity of MTB-CPR interaction and the functional basis of the physical interaction and cooperation, but also propose to take on the culturing of a model which seems particularly rewarding. This project is based on a multidisciplinary consortium coupling environmental microbiology, single-cell genomics, microscopy and phylogenomics, and combining recognized expertise in all models and disciplines involved.