Study Of Mineralization Mechanism Of Carbonates And Sulfates Mediated By Marine Microbes

The interaction between ubiquitous and minerals is ubiquitous in nature,and playes an important role in the evolution of the geological environment.Micobes can be involved in a variety of diagenetic processes in different geological environment,namely microbial mineralization.Microbial mineralization includes microbially controlled mineralization and microbially induced mineralization.A consensus is that microbial activities,cells and metabolites are the major factors to mediate polymorph,morphology,structure,elemental and isotope composition of biomineral.However,the exact role of microbes in mineralization is still not fully understood.In this dissertation,combined the microbiomineralization and biomimetic mineralization methods,we chose marine bacterium Shewanella piezotolerans WP3 and marine actinobacteria Brevibacterium sp.FXJ8.128 as the model strains to systematacially investigate the mineralization of microbiogenic carbonates and sulfates in molecular level.We studied the formation of aerobically incubated bacterial biomass-promoted disordered dolomite,and revealed the contribution of the bacterial biomass with high concentration and density of carboxyl and phosphoryl groups on disordered dolomite mineralization.Moreover,Shewanella piezotolerans WP3 was also used to investigate the effect of bacteiral various growth phases on the mineralization of Ca-Mg carbonates,and suggest that the chemistry of culture solution and metabolites excreted by bacteria(e.g.,low-molecular-weight organic matters with carboxyl)can be the key factors to influence the polymorph and morphology of mediated Ca-Mg carbonates.Besides the carbonate minerals,the ability of marine actinobacteria to mediate the formation of sulfate minerals(i.e.,barite)in low SO42-concentration system has been studies and we proposed that marine actinobacteria posseses the potential contribution to marine barite formation.The results in this dissertation can not only deepen the insight into the formation of microbial carbonates and sulfates,but also provide valuble informations to understand the origin of dolomite and barite in geological record.Several important results of this dissertation are summarized as follows:1.With the realization that the formation of low-temperature dolomite could involve the microbial activity,a new pathway to understand the origin and mechanism of dolomite is emerging.Although microbially mediated Ca-Mg carbonates and dolomite occur in some aerobic and high-salinity conditions,little information about the exact role of aerobic microbes is available.Herein,a strain of moderately halophilic bacterium,Shewanella piezotolerans WP3,was selected to study the involvement of aerobically incubated bacterial biomass in the Ca-Mg carbonate mineralization.Different biomass components were isolated from the bacterial cultures by a set of separation techniques,and used to mediate Ca-Mg carbonate mineralization under a carbon dioxide diffused system.The experimental results showed that bacterial cells play a dominant role in the formation of disordered dolomite.And the mineralization of the disordered dolomite can be attributed to the bare cells and bound extracellular polymeric substances isolated from the bacterial cells,most likely due to the promotion of high concentration and density of carboxyl and phosphoryl groups on the bacterial biomass.Hence,it does imply that bacterial biomass,even without the active microbial activities,can also play an important role in the formation of dolomite.Current results can not only extend the insight into the biologically influenced mineralization of Ca-Mg carbonates,but also shed light on the precipitation of disordered dolomite/dolomite in modern settings and geological records.2.Microbes,as the life entity like others,have a regularity of growth cycle.During the different growth phases,the number of microbes,metabolic activity and metabolite are dissimilar,and some physicochemical parameters of the surrounded microenvironment will change.These changes have different influences on the carbonates mineralization mediated by microbe,while the corresponding information is scared.Hence,Shewanella piezotolerans WP3 was chosen to investigate the influence of bacterial various growth phases on carbonate mineralization under simulative marine environment(i.e.,with 3.4%salinity,10 mM Ca2+ concentration and Mg/Ca= 5).The results of microbiomineralization showed that differ from the spindle-like aragonite as the products occurring in the lag,logarithmic and stationary phases,a kind of pillow-like high-Mg calcite with ca.20 mol%Mg can be obtained in the final decline phase.It indicates that bacterial various growth phases have different impacts on the formation of carbonates mineralization.According to the changes of solution chemistry and compositions,we proposed that the precipitation of aragonite during the first three growth phases could attribute to the high concentration of Mg2+in the biomineralization system,which can inhibit the nucleation and growth of calcite and facilitate the formantion of aragonite under low supersaturation condition.At the final decline phase,the increase of pH values and production of CO2 as the results of bacterial metabolism may help to achieve the required instantaneous supersaturation of calcite precipitation under high Mg/Ca ration(i.e.,Mg/Ca=5),which can overcome the inhibitation of Mg2+ and form the calcite.Furthermore,the results of biomimetic mineralization suggest that the production of low-molecular-weight organic metabolites may also be the factor to control the formation of pillow-like high-Mg calcite.Therefore,these findings will be helpful to understand the coexistence of different Ca-Mg carbonate phases in microbial mats,and provide new insights into the microbiogenic cabonates precipitation in nature.3.Marine barite usually appear in the waters and sediments with high biological productivity,and it is proposed that the metabolic activities of microorganisms in the oceans play an important role in the formation of barite.However,the effect of marine actinobacteria on barite deposits is still not clear,even though actinobacteria is ubiquitous in marine environment.Hence,a strain of marine actinobacteria,Brevibacterium sp.strains FXJ8.128,was chosen in this study as a model strain to investigate its ability to induce barite precipitation.The results show that strain FXJ8.128 can mediate the precipitation of barite in low-sulfate condition.According the results of a series of characterizations(i.e.,FESEM?EDX?XRD?TEM?HRTEM?SAED and synchrotron radiation soft X-ray image),the barite precipitation can be described as a multistep process.That is a kind of amorphous P-rich precursors firstly forms on or around cell surfaces,then the replacement of phosphate by sulfate will gradually occur.Meanwhile,due to the self-protective property of FXJ8.128,the minetalized products will peel off the active cell surfaces,eventually forming spherical barite crystal away from the cells.Therefore,our study provides the important information to investigate the role of marine actinobacteria in barite mineralization,indicating the barite mediated by marine actinobacteria has potential contribution to mairne barite formation.Additionally,based on the ancient lineage of actinobacteria and the low-sulfate conditions of Archean oceans,our study suggests that the formation of barite mediated by marine actinobacteria may also occur in the early marine environment of the earth,offering a possible clue to study the origin of ancient barites.