Two distinct pathways lead Bacillus thuringiensis to commit to sporulation in biofilm
Résumé
The spore-forming bacterium Bacillus thuringiensis is an efficient biofilm producer, responsible for persistent contamination of industrial
food processing systems. B. thuringiensis biofilms are highly heterogeneous bacterial structures in which three distinct cell types controlled by
quorum sensing regulators were identified: PlcR-controlled virulent cells, NprR-dependent necrotrophic cells and cells committed to sporulation,
a differentiation process controlled by Rap phosphatases and Spo0A-P. Interestingly, a cell lineage study revealed that, in LB medium or in insect
larvae, only necrotrophic cells became spores. Here we analyzed cellular differentiation undertaken by cells growing in biofilm in a medium
optimized for sporulation. No virulent cells were identified; surprisingly, two distinct routes could lead to differentiation as a spore in this growth
condition: the NprR-dependent route, followed by the majority of cells, and the newly identified NprR-independent route, which is followed by
20% of sporulating cells.