Property And Molecular Mechanism Of 2-MIB Biodegradation

2-Methylisoborneol(2-MIB)is one of the typical odorants,posing a serious threat to the safety of potable water.At present,domestic and foreign researches in 2-MIB removal mainly focus on ozonation and activated carbon absorption technology in ozone-biological activated carbon process,however,the biodegradation of 2-MIB has seldom been studied.In this study,four strains capable of removing 2-MIB efficiently were isolated from the activated carbon in the sand filter of the ninth plant of Beijing Waterworks Group through long-term domestication.They were identified to be Shinella zoogloeoides,Bacillus idriensis,Chitinophagaceae bacterium and Pseudomonas mandelii.The factors affecting the degradation efficiency of 2-MIB by the four strains in oligotrophic conditions were studied,including temperature,pH,dosage of bacteria,initial concentration of 2-MIB and addition of other carbon source.The four kinds of bacteria could utilize 2-MIB as nutrients more efficiently at 20-35? under neutral or alkaline conditions and could degrade 2-MIB at ng/L,?g/L and mg/L levels.The biodegradation of 2-MIB was improved with the presence of external carbon for Bacillus idriensis and Chilinophagaceae bacterium.The Bacillus idriennsis,Shinella zoogloeoides,Chitinophagaccae bacterium and Pseudomonas mandelii could grow stably in mineral salts medium of 2 mg/L 2-MIB,with the specific growth rates(?)were 0.0136 h-1,0.0088 h-1,0.0075 h-1,0.0095 h-1,respectively.When a high concentration of external carbon source existed,the degrading bacteria could quickly adapt to the environment and grow much faster.After the strains were mixed,the growth rates of the four kinds of degrading bacteria were decreased to different degrees.The ? of Shinella zoogloeoides was significantly decreased when growing with any other degrading bacteria,while Bacillus idriensis and Pseudomonas mandelii had minor changes in ? and were relatively dominant strains when growing together with other degrading bacteria.The degradation of 2-MIB by the four kinds of bacteria in mineral salts medium with 2-MIB are in accordance with a pseudo first-order reaction.Degrading bacteria dosage,2-MIB concentrations and external carbon source will not change its reaction kinetics.The degradation processes of the four strains in the treated river water containing 2mg/L,50?g/L and 500ng/L 2-MIB also conform to pseudo first-order reaction kinetics.The degradation products of 2-MIB by each degrading bacteria were analyzed.The degradation products by Pseudomonas mandelii and Bacillus idriensis were 2-Methyl-2-bornene and 2-Methylenebornane,respectively,both of which were dehydrated product of 2-MIB.In order to explore the mechanism of biodegradation of 2-MIB from the perspective of proteomics,the enzymes of degrading bacteria were isolated through ion exchange chromatography.A functional dehydrating enzyme that has never been reported was isolated from Pseudomonas mandelii.The catalytic action of this enzyme was consistent with the biodegradation pathway of 2-MIB.The primary structure,secondary structure,spatial structure and the binding site of the enzyme were analyzed and speculated.This dehydratase contains a conserved NAD binding site and one unknown binding domain.It is speculated that this domain may participated in the binding of 2-MIB and catalyze the dehydration of 2-MIB.