Og-Mediated Photodynamic Inactivation Mechanism For Ablation Of Bacteria And Biofilms Augmented By Potassium Iodide

The formation of pathogenic microorganisms and their biofilms on food contact surfaces not only endanger human health,but also destroy resources and environment,resulting in serious economic losses.Our previous studies had shown that octyl gallate（OG）,as a food antioxidant,exhibited high efficiency and broad-spectrum synergistic bactericidal activity,which was expected to be applied in different food scenarios.Recently,we found for the first time that potassium iodide（KI）had a strong synergic effect on OG mediated PDI,especially on the efficient clearance of food-borne harmful bacteria biofilms.However,the specific potentiated mechanism remains unclear.This work aimed to develop a novel method to potentiate the antibacterial and antibiofilm efficiency of PDI.From the perspectives of"photochemical pathways"and"composition of photochemical products and mode of interaction with biological and signaling molecules".The potentiated mechanism of antibacterial and antibiofilms was further explained at the molecular level.The main results were as follows:（1）To investigated the bactericidal effect of KI potentiated OG mediated PDI.The effect of PDI on Escherichia coli and Staphylococcus aureus depended on the concentration of OG and KI and the light dose.KI potentiated OG-mediated PDI in a dose-dependent manner.The ability to kill living cells under the blue light（BL）was demonstrated within 5 min（10⁷ CFU/m L E.coli:0.15m M OG+250 m M KI,10⁶ CFU/m L S.aureus:0.075 m M OG+150 m M KI）.（2）To investigated the KI potentiated OG mediated elimination of biofilm by PDI.It not only had a good eradication on mature biofilm,but also had a strong inhibition on biofilm formation.BL irradiation only 5 min increased the biofilm inhibition rate by 69%（0.05 m M OG+100 m M KI+BL 5 min）.The biomass of mature biofilm decreased by 80%after 10 min BL irradiation（0.1 m M OG+100 m M KI）.There were no viable bacteria in the superneant of the biofilm,and the number in the biofilm decreased significantly（>6.4 Log CFU/m L）.3D CLSM showed a large number of dead colonies,and the biofilm became thin and broken.（3）The photochemical pathway,which was the mechanism of KI potentiated OG on PDI,was investigated.The specific hydrophobic tail of OG combined with cell membrane to achieve transmembrane penetration.And it formed quinone under the dual action of autooxidation and photooxidation.Quinones underwent electron and energy transfer from ground state transitions and spin reversals to third excited state by photon absorption.And then,electron transfer（type I photochemical pathway）and energy transfer（type II photochemical pathway）are carried out,and further reacted with oxygen to form reactive oxygen species（ROS）.Type Ⅰ photochemical pathway:Electrons were transferred to O₂ to form O₂^·-,H₂O₂,·OH;Type Ⅱ photochemical pathway:Energy transfer to O₂ to form ¹O₂;TypeⅢphotochemical pathway:In the absence of oxygen,firstly,OG was inserted into cells,which destroyed membrane integrity,and interacted with DNA to form stable complex.Secondly,KI further damaged cells membrane through hyperosmotic pressure,and cell contents leaked out.Finally,intracellular photosensitizers transferred electrons directly to I^-and form I^·In addition to oxidizing biological targets,ROS can also oxidize KI to form HOOI₂^-,which was decomposed into I₂^·-,HOO·,H₂O₂ and I₂.Then,I₂ underwent electrophilic substitution with OG,and the iodine-substituted intermediates decomposed under BL,to formed free radicals.These ROS and reactive iodine species（RIS）can attack multiple targets in bacteria nonspecifically.Furthermore,among these short-lived and long-lived active species,the short-lived active species had stronger bactericidal effect.（4）The biomolecular interaction,which was the mechanism of KI potentiated OG on PDI,was investigated.Oxidation of ROS and RIS leaded to degradation of cell membrane proteins,cleavage of genomic DNA,and eventually cell death.More importantly,RIS promoted the cleavage of extracellular e DNA in the biofilm,effectively collapsing the biofilm;At the same time,the quorum sensing signaling molecules（3-oxo-C12-HSL）were degraded,so that the quorum sensing system cannot be activated,effectively avoiding repeated contamination of the biofilm.