Bacterial Extracellular Carbonic Anhydrase Catalyzes The Formation Of Carbonate Minerals

Microbial mineralization is an important geochemical process on the Earth's surface.Researches on the mechanism of carbonate mineralization in the presence of microorganisms are of great significance for the global carbon cycle,soil formation and evolution and other related scientific issues.There have been many reports on the formation of carbonate precipitates under microbial interactions.Some of the researchers believe that bacterial extracellular carbonic anhydrase(CA)is associated with the formation of carbonate minerals.However,the mechanism by which CA promotes carbonate mineralization is not yet clear.In this paper,five series of mineralization experiments were carried out using two kinds of extracellular carbonic anhydrase(CA)secreted by Arthrobacter sp.and Lysinibacillus sp.as the active substances.The X-ray diffraction(XRD),scanning electron microscopy(SEM),inductively coupled plasma optical emission spectrometer(ICP-OES)and other advanced equipment were used to study the formation of carbonate minerals promoted by bacterial extracellular carbonic anhydrase,and discussed its mechanism.The results of this study can be summarized as follows:(1)Under the action of MF-2 strain CA,61.3 mg precipitate was formed in 100 ml solution at 120 h,and 46.3 mg precipitate was formed in 100 ml solution at 192 h under the action of GW-2 strain CA.The results of treatment with 30%hydrogen peroxide show that carbonate minerals are the main components of the above precipitates.Carbonate minerals accounting for the total precipitate of 84.5%and 86.6%,respectively.The precipitate formed by the control experiment was significantly less than the CA experiment,and it was mainly composed of organic matter.(2)The calcite + vaterite was formed under the condition of extracellular CA activity(1.39 U/L)of MF-2 strain,and calcite was formed under low activity(0.06?0.5 U/L)of MF-2 strain.While the carbonate minerals formed by the extracellular CA(11.52×10-2U/L)of GW-2 strain formed only calcite.This may mean that CA activity has an effect on the type of carbonate mineral.(3)Whether the MF-2 strain or GW-2 strain extracellular CA,regardless of the level of CA activity,the formation of mineral morphology are relatively single The morphology of the minerals formed by the action of extracellular CA includes rhombohedral,spherical and hemispherical,in which rhombohedral minerals dominate.That is,mineral morphology may be independent of CA activity and origin.(4)The main mechanism of CA to promote carbonate mineral precipitation is its acceleration to CO2 hydration reaction.The CO2 participate in the reaction mainly comes from air.