Inactivation by Pulsed Light of Bacillus subtilis Spores with Impaired Protection Factors.

The resistance to pulsed light (PL) of spores of Bacillus subtilis strain 168 and of strains with mutations increasing sensitivity to UV-C or affecting spore structure was evaluated and compared to resistance to continuous UV-C and moist heat, in order to reveal original mechanisms of inactivation by PL. Spores of B. subtilis strain 168 (1A1) and eight mutant strains (sspA, sspB, sspAB, cotA, gerE, cotE, uvrA and recA) were exposed to PL (up to 1.77 J cm ), continuous UV-C (up to 147 mJ cm ) and moist heat at 90°C. Spores of the strains lacking proteins linked to coat formation or structure (cotA, gerE and cotE) were markedly more sensitive to PL than 1A1, while their sensitivity to continuous UV-C or to moist heat was similar to the one of strain 1A1. Coat proteins had a major contribution to the resistance of B. subtilis spores to PL irradiation characterized by short-time and high-energy pulses of white light in the wavelengths 200-1100 nm. In contrast the role of coat proteins to UV-C or to moist heat resistance was marginal or null.