Conference: Alexandre d'Halluin 7/11/25

Post-transcriptional regulation of a key sigma factor expression controls spore morphology in Bacillus subtilis

7 novembre 2025 @ 11 AM

Alexandre D’Halluin
UMR 8261 - CNRS/Université Paris Cité
Maturation et Dégradation des ARN
Laboratoire d’Expression Génétique Microbienne
Institut de Biologie Physico-Chimique 

Sporulation is a pathway conserved in some Gram-positive bacteria which leads to the formation of a highly resistant and dormant bacterial state called endospore, allowing the bacteria to survive to extreme environmental conditions for millions of years. In the model organism B. subtilis, sporulation allows the bacteria to resist to high stress conditions such as nutrient deprivation, heat, desiccation or radiation. The developmental program is known to be highly regulated at the transcriptional and post-translational level, which has been studied for decades. Bacterial RNA degradation mediated by ribonucleases is important for controlling gene expression through a variety of cleavage mechanism. A few have been shown to be expressed specifically during sporulation, while their mechanism and function during the developmental program are poorly understood.

Among factors involved in RNA degradation, we have identified one key factor of the spore morphology regulation, KapD, a ribonuclease exhibiting a 3’-exonuclease activity and specifically expressed during sporulation of B. subtilis within the mother cell. Deletion of the kapD locus or inactivation of its catalytic site strongly decreases the adhesiveness of the outer coat and crust layers of the endospore. Using dual-color fluorescent microscopy, we showed a dynamic assembly of the protein into the spore crust layer in a similar way to outer spore coat proteins, mediated by a direct interaction with the crust protein CotY. We identified a key developmental transcriptional regulator, sigK mRNA, as the main substrate of KapD. In fine, we provide evidence that KapD controls the timing of expression and activation of SigK prior to its sequestration within the spore crust layer.