Newly identified SpoVAF/FigP complex: the role in Bacillus subtilis spore germination at moderate high pressure and influencing factors

The SpoVAF/FigP complex, a newly identified dormant spore ion channel, has been shown to amplify the response of germinant receptors (GRs) to nutrient germinants. However, its contribution to high-pressure-induced germination remains unexplored. In this study, we discovered that the 5AF/FigP complex played an important role in the GR-dependent germination of Bacillus subtilis spores under moderate high pressure (MHP) by facilitating the release of ions, such as potassium (K⁺), a mechanism in parallel with its role in nutrient-induced germination. Despite its predicted function as an ion channel, the 5AF/FigP complex failed to be activated by MHP in the absence of GerA-type GRs. We quantitatively examined the factors that influence the 5AF/FigP complex's function in MHP-induced germination using modeling and fitting techniques. Our results indicated that the complex's amplification effect was both enhanced and accelerated as pressure levels increase from 50 to 200 MPa. However, raising the MHP treatment temperature from 22°C to 30°C only speeded up the complex's function without enhancing its effectiveness. Moreover, extreme conditions of higher pressure (300 MPa) and temperature (34°C-37°C) could diminish the complex's functionality. Additionally, the amplification effect was weakened in spores produced at both elevated and reduced sporulation temperatures. Taken together, our findings highlight the essential role of the 5AF/FigP complex in boosting the efficiency of MHP-induced germination. This revelation has enriched our understanding of the intricate mechanisms underlying GR-dependent germination in Bacillus spores, offering valuable insights that can be utilized to refine the germination-inactivation strategies within the food industry.

Importance: High-pressure-induced spore germination has been discovered for more than half a century, but the signal transduction pathway of the process still needs to be refined. In this study, for the first time, we revealed the role of the newly identified SpoVAF/FigP complex in high-pressure-induced spore germination, as well as the factors influencing its function in this process. The new findings in this work not only enhance the theoretical understanding of spore germination mechanisms under high pressure but also pave the way for developing novel strategies to inactivate spores during high-pressure food processing, a technology that is gaining popularity in the food industry as a promising non-thermal preservation method.