Effects Of Goethite On The Attachment And Aggregation Behavior Of Pseudomonas Aeruginosa And Its Resistance To Disinfectants

Drinking water bacteria prefer to attach to surfaces as biofilms for self-protection when confronted with changing environmental stresses.However,the knowledge about bacterial attachment and aggregation behaviors onto particles and their impacts on the resistance to unfavorable environments,especially under disinfection and nutrient limitation stresses,remains unclear.Therefore,this study aimed to investigate the protection effects of particulate matters from disinfectants,and to unravel the mechanisms of goethite-mediated aggregation and extracellular polymer substances（EPS）-shaped protection from disinfectant for the Pseudomonas aeruginosa and over-secreted mutant strains.This study would provide theoretical guidance for the control of bacterial growth in drinking water systems.Firstly,the protective effect of goethite on wild-type and mutant Pseudomonas aeruginosa at various nutrient and disinfectant circumstances was investigated via a simulated experimental system.The presence of disinfectants（1.0 mg/L chlorine and2.0 mg/L chloramine）inhibited bacterial growth,while the presence of goethite promoted bacterial resistance to the disinfectants.The survival of wild strains increased by 2 times at 2 h following the addition of goethite at initial chlorine of 1.0mg/L.Increasing nutrient concentrations enhanced this protective effect,while the comparison of the survival rates between the two strains revealed that the mutant with excessive alginate secretion had greater resistance to disinfectants.The results showed that goethite had a protective effect on bacteria upon exposure to disinfection,while augmented EPS production and nutrient supply improved the protective effect of goethite.Secondly,the effect of goethite on the attachment and aggregation behavior of Pseudomonas aeruginosa at various disinfectants was examined.The results showed that the presence of goethite stimulated bacterial aggregation,with the cluster size of the WT strain increased by twofold after 6 h exposure to 2.0 mg/L chloramine at the sufficient nutrient condition.In addition,reducing nutrient supply encouraged bacterial aggregation on the goethite surface.Meanwhile,the mutant strain yielded a higher rate of aggregate formation as compared to the WT strain.This indicated that goethite facilitated the attachment and aggregation of Pseudomonas aeruginosa under disinfection,while limited nutrient and enhanced EPS production further promoted the attachment and aggregation behaviors.Finally,to further analyze the mechanism of the aggregation and protective effects of goethite on Pseudomonas aeruginosa under disinfection stress,the effects of goethite dosing on nutrient adsorption,disinfectant decay,and the functional group alteration following bacteria-goethite interaction were investigated.The results showed that the addition of goethite adsorbed organic matter and thereby promoted bacterial aggregation.Meanwhile,it yielded a faster decay of disinfectants.In addition,the stretching vibration peak of bacterial polysaccharide C=O was observed to shift from 1080 cm^-1 to 1053 cm^-1 after the bacteria-goethite interaction,with the O-H infrared spectrum of goethite shifting from 898 cm^-1 to 893 cm^-1.The results indicated that goethite promoted bacterial adhesion,aggregation and resistance to disinfectants through adsorption of organic matter and reaction with disinfectants,as well as through O-H reaction with polysaccharide C=O functional group of bacteria.