| Carbonate and silicate weathering,microbes involve in,is an important part of the surface biogeochemical processes,which has a profound impact on material recycling of Earth surface and the formation and evolution of topography.Therefore,it attracts widespread attention of scholars in the field of microbial ecology,geology,microbiology and biogeochemistry.The main forces,already known,are secretion of organic acids,chelation,redox and biomechanical role.However,the forces mentioned above are at cellular level and it is still ambiguous that how microbes affect mineral weathering at molecular level.That is to say,the molecular mechanism of the interaction between microbes and minerals and the gene expression regulation remains to be discussed.Recently,some researches show that enzymes not only regulate metabolism but also directly participate in the process of mineral dissolution.One kind of enzyme,carbonic anhydrase(CA),widely present in various organisms,such as archaea,bacteria,fungi and mammalian.It is capable of catalyzing the hydration reaction of CO2 and the reverse reaction.The produce,H+,can accelerate the dissolution of carbonate or silicate,and the mineral dissolution in turn affects carbon cycle.Therefore,it is worth studying the function of CA.Bacillus mucilaginosus commonly known as silicate bacteria lives in the surface of rocks or soils with a strong ability to weather minerals.Five kinds of CA genes are detected in the B.mucilaginosus K02 genome through genome sequencing.In view of this,real-time fluorescence quantification PCR(RT-qPCR)was used to detect whether the expression of CA genes is related to carbonate or silicate weathering.This study can explore whether CA participates mineral weathering process at the molecular level.The results showed that these two kinds of minerals can significantly induce expression of B.mucilaginosus CA genes.The role of microbial CA on minerals weathering was further confirmed,after the clones of five types of CA genes constructed.Induction of protein expression was induced,and the activity was measured.One kind of CA was used to study the function of heterologously expressed protein promoting the dissolution of calcite and wollastonite.The results showed that the dissolution rate of both minerals was accelerated.It suggested that microbial CA can indeed be directly involved in mineral weathering.A self-designed device was used to set different CO2 concentrations and investigate whether CO2 concentration impact the function of CA in mineral dissolution process.The results showed that the role of CA was weakened at high CO2 concentration.Meanwhile,induced mineralization experiment verified that single CA protein played a role in accelerating CaCO3 formation at ambient CO2 concentration and the importance decreased at 3.9%CO2 concentration.In view of this,with the evolution of the Earth and decreased CO2 concentration,the role of microbial CA may have become increasingly more apparent and important as terrestrial surface rocks have evolved.Some researches shows redundant genes gradually lose during biological evolution,retained genes transcribe or translate to RNA or the corresponding protein playing a physiological function under certain conditions.According to previously study about the weathering of K-bearing mineral by Aspergillus(Aspergillus fumigatus and Aspergillus niger),only one kind of differentially expressed CA gene was presented,while the role of the other was unclear.Two different sequences of CA genes in A.nidulans genome simplifies the study of gene function differentiation.We explored that whether one of two CA is preferred when it grows in certain circumstances(lack of mineral nutrients and CO2 concentration change).Expression levels of two CA genes was analysed using RT-qPCR and Northern blot.The results imply that CA1 is involved in mineral weathering and CA2 is related to CO2 adaption.To further verify that CA1 can promote silicate dissolution,the clone of CA1 gene was constructed and the induction of protein expression was carried out.Purified CA1 protein accelerated biotite and wollastonite dissolution.It suggested that the directional selection of the A.nidulans CA isozyme could ease some of the adverse effects brought about by external changes in the environment.It could also help A.nidulans avoid the waste of materials and energy caused by the genetic over-expression.CO2 concentration continues to rise seriously,which affects the survival of mankind.Minerals affect the regulation of gene expression while at the same time affect the carbon cycle.Changes of biological metabolic in turn act on processes of mineral dissolution and re-deposition,which also closely links with atmospheric CO2 cycle.Agricultural production is the embodiment of human civilization,so far,a few thousand years of history.We tried to combine the theoretical knowledge and agricultural production in order to increase atmospheric CO2 fixation or reduce CO2 release from soil respiration.We study the impact on carbon sinks by adding mixed dolomite and K-feldspar minerals into soil.Experimental results showed that inorganic carbon and the soil organic carbon increased to some extent.This not only provides a theoretical basis for subsequent mineral-organic fertilizer experiments,but also shows an effective way for the implementation of green agriculture.To sum up,in this paper,the following conclusions are drawed:1.CAs of B.mucilaginosus and A.nidulans are directly involved in mineral weathering;2.single CA can promote the dissolution of carbonates and silicates and carbonates formation.3.CO2 concentration affects the role of CA(negative correlation);4.Mixed minerals(dolomite and feldspar)can promote the formation of carbon sinks.The results do nothing but forge a deep understanding and awareness on molecular mechanisms of mineral weathering,microbes involve in,during biogeochemical cycle process.The results are important references for the subsequent study of natural CO2 sequestration. |
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