UV-C and hydration state drive Pulsed Light-induced proteome damage in Bacillus pumilus spores

Imed Dorbani ¹ Jean ARMENGAUD ² Frédéric CARLIN ¹ Catherine Duport ^3*

• ¹ INRAE PACA, Avignon, France
• ² Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Paris, Île-de-France, France
• ³ University of Avignon, Avignon, France

Pulsed light (PL) is a non-thermal processing technology that inactivates microorganisms through pulses of polychromatic light, including ultra violet-C (UV-C). Here, we investigate the impact of PL on the spore proteome of the bioindicator Bacillus pumilus DSM492 (ATCC 27142), comparing it to UV-C 254 nm exposure. Spores were either suspended in water or sprayed onto a polystyrene surface and subjected to PL or UV-C at fluences achieving inactivation with a 5-log reduction and a >7-log reduction. Our findings reveal that the proteome of B. pumilus exhibits higher susceptibility to PL, characterized by a ~6-fold increase in the number of proteins with decreased abundance, in spores suspended in water compared to spores sprayed on a polystyrene surface. By comparing the proteomic profiles after PL and UV-C exposure, we showed that the impact of PL on the proteome in water is due to UV-C 254 nm, whereas on the polystyrene surface, UV-C 254 nm has no significant effect. Interestingly, proteins particularly affected by PL exhibited a higher content of photosensitive amino acids such as tryptophan, histidine, tyrosine, cysteine, and methionine, suggesting that oxidation and photoreactivity contribute to their degradation. While the overall inactivation rate could not be directly linked to the extent of proteome damage, we demonstrated that crucial core proteins related to DNA or RNA protection and repair are specifically targeted by PL.