High salinity sporulation in Bacillus subtilis results in coat dependant enhanced resistance to both heat and hydrogen peroxide

In natural niches, spore-formers encounter non-optimal sporulation conditions that can affect spore resistance properties. However, while the influence of sporulation temperature on spore behaviour has been widely studied, knowledge concerning the influence of other factors such as water activity (a_w) is scarce. We previously reported that reducing the a_w of the sporulation medium from the optimum (a_w 0.99; S_control spores) to 0.98 using sodium chloride (S_salt spores) increased the wet heat resistance of Bacillus subtilis 168 spores. The present work aimed to examine the mechanism behind the increased heat resistance observed in S_salt spores. The crust morphogenetic protein CotY was required for the increased heat resistance and increased resistance to H₂O₂ in S_salt spores. Label-free quantitative proteomics of S_control and S_salt spores revealed markedly different protein profiles. Specifically, S_salt spores displayed significant increases in abundance of proteins involved in redox homeostasis, as well as changes in coat structural proteins, some of which are involved in protein-protein interactions. This work advances our understanding of how the coat modulates resistance in bacterial spores, helping develop effective control strategies against problematic spore populations due to occurring environmental changes.