ABSTRACT
Microbial surface contamination of equipment or of food contact material is a recurring problem in the food industry. Spore-forming bacteria are far more resistant to a wide variety of treatments than their vegetative forms. Understanding the mechanisms underlying decontamination processes is needed to improve surface decontamination strategies against endospores potentially at the source of foodborne diseases or food-spoilage. Pulsed light (PL) with xenon lamps delivers high-energy short-time pulses of light with wavelengths in the range 200 nm-1100 nm and a high UV-C fraction. Bacillus subtilis spores were exposed to either PL or to continuous UV-C. Gel electrophoresis and western blotting revealed elimination of various proteins of the spore coat, an essential outer structure that protects spores from a wide variety of environmental conditions and inactivation treatments. Proteomic analysis confirmed the elimination of some spore coat proteins after PL treatment. Transmission electron microscopy of PL treated spores revealed a gap between the lamellar inner spore coat and the outer spore coat. Overall, spores of mutant strains with defects in genes coding for spore coat proteins were more sensitive to PL than to continuous UV-C. This study demonstrates that radiations delivered by PL contribute to specific damage to the spore coat, and overall to spore inactivation.
Subject(s)
Bacillus subtilis/metabolism , Bacillus subtilis/radiation effects , Capsid Proteins/metabolism , Capsid Proteins/radiation effects , Decontamination/methods , Light , Bacillus subtilis/genetics , Cell Wall/metabolism , Cell Wall/radiation effects , Decontamination/standards , Proteomics , Spores, Bacterial/physiology , Spores, Bacterial/radiation effectsABSTRACT
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-2 ), continuous UV-C (up to 147 mJ cm-2 ) 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.
Subject(s)
Bacillus subtilis/radiation effects , Bacterial Proteins/metabolism , Gene Expression Regulation, Bacterial/radiation effects , Light , Spores, Bacterial/radiation effects , Bacillus subtilis/physiology , Bacterial Proteins/genetics , DNA Damage , DNA Repair/physiology , DNA, Bacterial/genetics , Mutation , Spores, Bacterial/physiologyABSTRACT
The photoprotective potential of fungus pigments was investigated by irradiating conidiospores of three Aspergillus niger strains possessing the same genetic background, but differing in their degree of pigmentation with pulsed light (PL) and monochromatic (254 nm) UV-C radiation. Spores of A. niger MA93.1 and JHP1.1 presenting, respectively, a fawn and a white pigmentation were more sensitive to PL and continuous UV-C radiation than the wild-type A. niger strain N402 possessing a dark pigment. Both spores of the dark A. niger N402 and the fawn-color mutant were equally resistant to moist heat at 56°C while spores of the white-color mutant were highly sensitive. These results indicate that melanin protects pigmented spores of A. niger from PL.
