High pressure germination of Bacillus subtilis spores with alterations in levels and types of germination proteins

Aims: Examine effects of different levels and types of nutrient germinant receptors (GRs) and other germination proteins on Bacillus subtilis spore germination by a moderate high pressure (mHP) (150 megaPascals (MPa)) that triggers germination through GRs, and a very high pressure (vHP) (550 MPa) that triggers spore germination independent of GRs. Methods and Results: The Moderate HP (mHP) and vHP germination kinetics of B. subtilis spores with large variations in levels of GRs and other germination proteins, including the GerD protein and the SpoVA proteins that comprise a spore membrane channel that is likely opened by vHP were measured. Conclusions: GR levels were the major factor determining mHP germination rates. However, other factors modulated mHP germination rates including (i) relative levels of individual GRs (GerA, GerB, GerK), as mHP affected different GRs differently; (ii) levels of a recently identified small protein that may be a GR subunit; and (iii) a dominant negative mutation in gerD that eliminates GR-dependent nutrient germination. In contrast, the alterations in germination proteins had no major effect on vHP germination, except for reduction of SpoVA protein levels. Significance and Impact of the Study: With the increasing use of HP for food processing, this study provides new information on factors that modulate HP germination of spores for potential application of HP technology to achieve food sterility.