Isolation and characterization of superdormant Bacillus subtilis spores under high hydrostatic pressure at 200 MPa and 500 MPa

Abstract

High hydrostatic pressure (HHP) (200 MPa/500 MPa) superdormant (SD) spores were isolated and characterized for germination and resistance properties. Compared with untreated spores, two-hundred MPa-SD spores showed germination defect with L-alanine, AGFK, dodecylamine, 200 MPa or 500 MPa. Meanwhile, they exhibited elevated resistance to 93 °C and UV_{254 nm} with decimal reduction time (D-value) increased by 2.7 and 1.5 fold respectively, reduced resistance to 0.22 M HCl and 3.2 M H₂O₂ with D-value decreased by 1.4 and 1.3 fold respectively, and no change in resistance to 0.83 M formaldehyde and 0.34 M NaClO. Five-hundred MPa-SD spores showed germination defect with 500 MPa, no change in germination with L-alanine, AGFK or 200 MPa, but increased germination efficiency with dodecylamine. Accordingly, their resistance to 0.34 M NaClO and UV_{254 nm} elevated with D-value increased by 1.8 and 1.3 fold respectively, while resistance to 93 °C, 0.22 M HCl, 0.83 M formaldehyde and 3.2 M H₂O₂ reduced with D-value decreased by 2, 1.4, 1.4 and 2.3 fold respectively. These properties were noninheritable as re-sporulated spores from SD spores showed identical germination behavior compared to initial untreated spores. Proteomics analysis revealed that the mechanism of SD spores' superdomancy was likely attributed to the variation of coat proteins and SASPs, and inner membrane modifications.

Industrial relevance

It has long been acknowledged that the existence of SD spores greatly limits the successful application of HHP technology in low-acid foods. The data in this work provide valuable knowledge to understand the properties of SD spores under HHP, and thus hopefully can promote developing new strategies to eliminate bacterial spores in low-acid foods during industrial HHP processing.