Reduced Iron-containing Clay Minerals As Antibacterial Agents And Their Bactericidal Mechanism

Various natural clays that kill drug-resistant were documented in previous study and as a result,these clays have been proposed as antibiotic alternatives.Reduced iron-contaning clay minerals(RIC)are important components of natural antibacterial clays.One specific role that RIC play in the antibacterial activity is its capacity to buffer pH and promote the solubility of Fe2+ which is bactericidal.Here we showed that pure RIC could produce abundant hydroxyl radical(·OH)in near neutral pH upon air oxidation.At pH 6,1.25 g/L reduced nontronite(rNAu-2)was able to eliminate all E.coli within 24 hours.rNAu-2 is recyclable and toxic to multi-drug resisting pathogen.·OH,which was produced upon the air oxidaiton of structural Fe(?)in RIC,disrupted vulnerable cardiolipin mainly located in polar region of E.coli.The disruption of cardiolipin triggers the influx of solube Fe2+ participating lethal Fenton reaction resulting the accumulation of ROS in the polar region of E.coli and ultimately leads to cell death.Enhancing the interaction between RIC and pathogens may increase the antibacterial capability of RIC.Here,chitosan was intercalated to prepare positively charged rCNAu-2,which closely contacted with negatively charged E.coli.In comparison with negatively charged rNAu-2,rCNAu-2 produced less ·OH and released less soluble Fe2+ into solution,however,rCNAu-2 showed enhanced bactericidal capability.Further investigation revealed that rC-NAu-2 closely contacted with E.coli enhancing the utility of ·OH,which disrupt all major phospholipids of E.coli membrane,resulting in more Fe2+ influx and ROS accumulation.The antibacterial mechanism of RIC needs to be further elucidated.Here,the change of thiol-redox proteome and total proteome of E.coli were quantified by mass spectrometry-based shotgun proteomics.The reversable oxidation level of 53 cysteine sites from 51 proteins increased upon rNAu-2 treatment in which many proteins along with their redox-active functional sites were known critical in oxidative stress adaption of E.coli.Upon rNAu-2 stimulation,proteins related to heat shock response and transcription repression were up-regulated while proteins related to metabolic processes were down-regulated.Our proteomics data set is an invaluable source which provides insight for enhancing the bactericidal activity of RIC-type materials.