Figures (6)  Tables (0)

    • Figure 1. 

      Germination of A. acidoterrestris (A.t) and B. subtilis (B.s) spores induced by nutrient germinants under pH conditions. (a) DPA release from A. acidoterrestris spores induced by 10 mM L-alanine. (b) DPA release from A. acidoterrestris spores induced by 10 x AGFK; DPA release from B. subtilis spores induced by (c) 10 mM L-alanine, and (d) 10 x AGFK. Each experiment in the figure included three replicate groups.

    • Figure 2. 

      Germination of A. acidoterrestris spores under varying nutrient germinant concentrations and pH conditions. DPA release from heat-activated spores induced by different concentrations of (a) L-alanine, and (b) AGFK in pH 4 K-Hepes; DPA release from (c) heat-activated spores, and (d) non-heat-activated spores under pH 2–9 conditions in the absence of nutrient germinants; (e) DPA release of spores incubated in pH 4 and 7 systems at 4, 20, and 37 °C for 1, 3, 5, 8, and 12 d. (f) DPA release from spores was monitored in germinant-free sterile water and K-Hepes buffers at pH 4 and 7. Each experiment in the figure included three replicate groups.

    • Figure 3. 

      Optimization of heat activation conditions for A. acidoterrestris spore germination. (a) Heat resistance of A. acidoterrestris spores at 95, 90, 85, 80, 75, 70, and 65  °C for 60 min; (b) DPA release from spores after heat activation at 75, 70, 65, and 60  °C for 30 min in pH 4; (c) heat activation at 70 °C for 1, 5, 15, 30, 45, and 60 min; (d) spores were heat activated at 70 °C for 15, 30, 45, or 60 min, then divided into two groups: one was directly plated for colony enumeration, and the other underwent an additional 80 °C/30 min treatment prior to plating. Percentage of germinated spores was calculated as: (CFU after heat activation-CFU after 80 °C treatment)/CFU after heat activation × 100%; (e) DPA release from spores heat-activated at 70 °C for 15 min and incubated at 18, 25, 30, 37, and 42 °C; (f) viable counts of untreated spores and spores heat activated at 70 °C for 15 min in pH 4 and 7; (g) DPA release from spores heat activated at pH 4 or 7, then immediately incubated (IC) at 37 °C and pH 4 or 7. Each experiment in the figure included three replicate groups.

    • Figure 4. 

      Germination and viability of A. acidoterrestris (A.t) and B. subtilis (B.s) spores under HHP at various pH conditions. At 200 MPa/30 °C: (a) DPA release, and (b) colony counts of A. acidoterrestris spores; (c) DPA release, and (d) colony counts of B. subtilis spores. At 500 MPa/30 °C: (e) DPA release, and (f) colony counts of A. acidoterrestris spores; (g) DPA release, and (h) colony counts of B. subtilis spores. Each experiment in the figure included three replicate groups.

    • Figure 5. 

      Spontaneous germination and viability of A. acidoterrestris spores under acidic and neutral conditions. (a) After HHP (200 or 500 MPa/3 min/30 °C) , DPA release in the supernatant was measured immediately, the pellet was subsequently incubated at 37 °C to monitor DPA release over a 30 min period. (b) Colony counts of spores at pH 4 and 7 immediately after the HHP treatment. Each experiment in the figure included three replicate groups.

    • Figure 6. 

      Inactivation of A. acidoterrestris spores using germination-inactivation strategy. Spores were first subjected to heat activation at 70  °C for 15 min, followed by incubation at 37  °C for 1 h, then application of 80  °C/30 min or HHP (500 MPa/10 min). The second approach began with HHP treatment (200 Mpa/10 min or 500 MPa/10 min), followed by incubation at 37  °C for 1 h, then application of 80  °C/30 min or HHP (500 MPa/10 min). Control groups included untreated spores, spores treated only at 80  °C for 30 min, only at 200 MPa for 10 min, or only at 500 MPa for 10 min. Each experiment in the figure included three replicate groups.