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A recombinant Bacillus subtilis strain containing a plasmid encoding a luxAB fusion, which gave bioluminescence upon addition of an exogenous long-chain aldehyde as substrate for the endogenous luciferase enzyme, was used as test organism. Its populations were treated with 300 MPa for 20 min, or 600 MPa for 20 min at around room temperature, and this treatment is foreseen as a quality-friendly, non-thermal pasteurisation of foods. Besides the estimation of viable cell counts, the extent of pressure-induced germination and post-process development were investigated by phase-contrast microscopy, turbidimetry and luminometry. Increased heat sensitivity of pressurized spore populations was observed both by viable cell counting during a linearly programmed elevation of temperature and a simultaneous differential scanning calorimetry. This was related to pressure-induced germination of spores, although a small fraction remained ungerminated. The luciferase pool built into the spores during their formation seemed to have withstood pressurization. Spore germination was accompanied by the emergence of bioluminescence which also indicated sensitively the characteristic changes of metabolic activity running parallel with the development of untreated cell populations and that of the survivors of the hydrostatic pressure treatments when the cells were incubated in a nutrient broth.

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