The role of endospore appendages in spore-spore contacts in pathogenic bacilli

Species within the spore-forming Bacillus cereus sensu lato group are recognized for their role in food spoilage and food poisoning. B. cereus spores are decorated with numerous pilus-like appendages, called S-ENAs and L-ENAs. These appendages are believed to play crucial roles in self-aggregation, adhesion, and biofilm formation. By using both bulk and single-cell approaches, we investigate the role of S-and L-ENAs as well as the impact of different environmental factors in spore-to-spore contacts and in the interaction between spores and vegetative cells. Our findings reveal that ENAs, and particularly their tip fibrilla, play an essential role in spore self-aggregation but not in the adhesion of spores to vegetative cells. The absence of L-BclA, which builds the L-ENA tip fibrillum, reduced both S-and L-ENA mediated spore aggregation, emphasizing the interconnected roles of S-and L-ENAs. Increased salt concentrations in the liquid environment significantly reduced spore aggregation, implying a charge dependency of spore-spore interactions. By elucidating these complex interactions, our study provides valuable insights into spore dynamics. This knowledge can guide future studies on spore behavior in environmental settings and aids in developing strategies to manage bacterial aggregation for beneficial purposes, like controlling biofilms in food production equipment.