Chaperone protein DnaK-mediated regulation of spore coat assembly in Bacillus subtilis.

Bacterial spores pose a significant challenge to the food industry due to their ability to germinate from dormancy and their extreme resistance. Spores are encased by a multilayered proteinaceous structure termed the spore coat. Previous studies on spore coat assembly have predominantly focused on the interactions among coat proteins, while the involvement of broader protein quality control systems remains poorly understood. Here, we demonstrate that the molecular chaperone DnaK is essential for the proper assembly of the inner spore coat in Bacillus subtilis. Deletion of dnaK leads to mislocalization of key morphogenetic protein SafA, reduced accumulation of full-length SafA, altered transcriptional dynamics of spoIIID and sigK, and ultimately impaired coat integrity and function. Our findings reveal that DnaK facilitates spore coat assembly through both transcriptional and post-translational mechanisms, uncovering a previously unrecognized regulatory layer in spore coat morphogenesis.