Effects Of Water Freeze-thaw Cycles On Oxidation Of Mn(?) By A Manganese-oxidizing Bacterium

Manganese-oxidizing bacteria refer to the bacteria that can oxidize manganese(II)ions from divalent to trivalent or tetravalent.These bacteria are widely distributed and have different oxidation characteristics due to different environmental conditions.They play an important role in the biotransformation of manganese.Freeze-thaw cycles are a common phenomenon in the water environment in early spring and late autumn in Northeast China.Many studies have shown that freeze-thaw cycles can affect the metabolic activity and survival rate of microorganisms,thereby,influencing the biogeochemistry cycle of various elements mediated by microorganisms.However,it is still not clear about the oxidation of manganese(II)ions by manganese-oxidizing bacteria in the condition of water freeze-thaw cycles.The research on the effect of freeze-thaw cycles on the biogeochemistry cycle of manganese could reveal the key role of manganese-oxidizing bacteria in the process of manganese(II)ions oxidization,and provide a theoretical basis for the assessment of manganese pollution in the environment.This study focused on the effect of water freeze-thaw cycles on the process of a manganese-oxidizing bacterium oxidizing manganese(II)ions.First,the manganese-oxidizing bacterium was isolated and purified from coastal waters with freeze-thaw cycle characteristics by using the selective medium.Secondly,the influences of the freeze-thaw cycle on the manganese transformation during the process of manganese(?)irons oxidation were determined by comparing the changes in the concentrations of free manganese,adsorbed manganese,and oxidized manganese in the freeze-thaw cycle,low temperature and normal temperature systems in the laboratory.Finally,the effect of freeze-thaw cycles on manganese(II)ions oxidation by the manganese-oxidizing bacterium was revealed by measuring the number of bacterium,p H,total reactive oxygen species(ROS)concentration,and hydrogen peroxide(H₂O₂)concentration in the three systems,as well as analyzing the relationship between the above factors and manganese(II)ions oxidation in each system.The bacterium isolated belonged to Metabacillus,we named it Metabacillus sp.X.Its colony is white,circular,translucent,smooth and moist on the surface.The results suggested that the freeze-thaw cycles could significantly inhibit the growth of Metabacillus sp.X and the production velocity of ROS and H₂O₂.The existence of manganese(II)ions could promote the production of ROS.The relative analysis result showed that among the freeze-thaw cycles,the low and the normal temperature systems,the number of Metabacillus sp.X and the p H were the main factors that affected the transformation of the free manganese to the absorbed manganese while the p H and the ROS were the main factors that affected the transformation of the free manganese to the oxidized manganese.The freeze-thaw cycles could influence the indirect oxidation progress of the manganese regulated by p H and ROS.The oxidation of the manganese in the freeze-thaw cycles system was a comprehensive result of the effects of Metabacillus sp.X metabolism,absorption,direct and indirect oxidation...