Function, role, and control of gigantic bacterial roll

Objective

R-bodies are probably the largest organised intracellular proteinaceous structures in bacteria. They adopt a roll-like structure that occupies almost the entire cellular volume. Upon acidification, R-bodies extend telescopically up to 20 micrometres. First discovered in endosymbiotic bacteria, they were proposed to eliminate symbiont-free hosts, however their mechanism of toxicity remained unexplored. In addition, structures of similar composition and activity form ejectile defence organelles in Cryptomonads. Recently, we found that free-living environmental bacteria from the phylum Bacteroidota also produce R-bodies. In the Fun-ContRoll project we will study the assembly and conformational change mechanisms of these structures. We will investigate their mechanism of action and ask whether it depends on the extension or delivery of associated toxic effectors. To understand their biological role, we will explore hypotheses about their costs and benefits to the bacterial cell and to population. Alternatively, we will assess their role in establishing and maintaining the symbiosis. We will evaluate whether their biological role has pathogenic potential or, on the contrary, could help to eliminate parasitic species that cause disease and spread pathogenic bacteria. Finally, we will try to understand the strict regulatory mechanisms that controls the heterogeneity in the population, leading to a well-defined fraction of the population that produces these giant structures.