A Comparative Study Of Carbonate Precipitation Induced By Two Strains With Different Gram Properties

Carbonate minerals are the most widely distributed and common minerals in nature,and the relationship between carbonate minerals and microbial activity dates back 3.5 billion years.The researchers found that the minerals induced by microorganisms are originate from the metabolism of bacteria,which changes the physical and chemical conditions of the surrounding environment and the carbonate minerals of various forms and types were formed.Carbonic anhydrase secreted by bacteria has been proved to be biocatalytic for CO2 hydration to form HCO3-and CO32-,then accelerate the rate of carbonate precipitation and reduce the concentration of CO2 in the atmosphere.In addition,microbially-induced calcium carbonate precipitation has important significance in reducing heavy metal pollution in soil and lakes,restoring ornamental stone cultural relics,indicating environmental and climate change.However,so far,the specific mechanism of microbial involvement in carbonate mineral formation has not been thoroughly studied.Therefore,a series of mineralization experiments were performed by Bacillus cereus strain LV-1 and Curvibacer sp.strain HJ-1.They were inoculated in the same medium for microbial mineralization for 30 days,and extracellular polymers secreted by bacteria were used to conduct 120 h gas diffusion experiment in the same solution.During the experiment,the pH value,electronic conductivity and the ion concentration;the extracellular polysaccharide and carbonic anhydrase secreted by bacteria;minerals' types and forms and elements and the carbon isotope fractionation were determined and analyzed.Finally,the results of the study on microbial induction of hydrochloride mineral can be summarized as follows:(1)Bacillus cereus strain LV-1 and Curvibacter sp.strain HJ-1 both had the ability to induce carbonate mineral formation in the medium without CO32-.The total weight and crystal size of huntite induced by strain LV-1 in the process of mineralization experiment on 30 days were 26.5 mg and 40 ?m respectively.The total weight of huntite induced by strain HJ-1 in the process of mineralization experiment for 30 days was 14 mg and the crystal size was about 6?m.(2)The strain LV-1 and the strain HJ-1 both induced the formation of calcite in the medium of Mg/Ca=1;mainly induced the formation of huntite in the medium of Mg/Ca=5.(3)The mineral morphologies induced by strain LV-1 were quite different from those induced by strain HJ-1.The calcite induced by strain LV-1 showed irregular shape and cube shape;huntite was columnar,massive and globular.The calcite induced by strain HJ-1 was mainly short rod-shaped,dumbbell shaped and spherical;huntite was hexahedral shape,irregular shape,long plate shape.(4)Bacteria with different gram staining properties were all induced to form calcite,but the difference was that the strain HJ-1 of Gram-negative bacteria was more likely to be used as the nucleation template of minerals,leading to the formation of dumbbell-like minerals.The strain LV-1 of Gram-positive bacteria was more likely to cause irregular mineral formation.(5)Microbial metabolism affects the composition of carbon isotopes in minerals.The?13C value of the biotic calcite was-17.410‰,which was close to the ?13C=-14.704‰ of tryptone.Thus,it can be concluded that carbon precipitated by carbonate minerals mainly comes from tryptone.(6)Bacterial extracellular polymers could affect mineral species and morphology.The extracellular polymer secreted by strain LV-1 was more conducive to the formation of highmagnesium calcite,and most of them were cauliflower.The extracellular polymer secreted by strain HJ-1 was more beneficial to the formation of aragonite,which is prismatic and hemispherical.(7)There was a significant positive correlation between pH value and mineral weight in the culture medium,and a significant negative correlation between Ca2+ concentration and mineral weight,indicating that a higher pH value,namely the alkaline environment of the solution,was conducive to the formation of carbonate minerals,and the decrease of Ca2+concentration could indirectly indicate the formation of minerals.