| In recent years,environmental pollution caused by over-exploitation of mines has attracted wide attention.Iron oxidation and reduction play a key role in the formation of acidic mine environment.At present,studies have been carried out on the formation and dissolution of minerals by light,and photoelectrons produced by semiconductor minerals stimulated by light to promote microbial growth.However,it is not clear whether light can affect microorganisms and how light affects the iron cycle in which microorganisms participate.In this paper,an iron-reducing bacterium AMDY2-9-2 and an iron-oxidizing bacterium W-4-3 isolated from the acidic mine environment of Shizishan,Tongling,Anhui Province,were studied for their characteristics of reducing Fe(III)and oxidizing Fe(II)under or without illumination,and the effects of illumination on microorganisms invol-ved in iron oxidation cycle were analyzed at molecular level by iTRAQ technology.It is of great significance to understand the role of light in iron redox cycle and the influence of light on iron reducing bacteria and iron oxidizing bacteria in acidic environment.It is also expected to provide reference for the biorestoration and biotreatment of acidic mine environment.In the study of the effect of light on iron reduction,three groups of experiments were designed including viable bacteria group,dead bacteria group and aseptic group.Each group was divided into light and non-light conditions.The growth cycle,pH,Eh,Fe2+,SO42-concentration under or without light were studied with AMDY2-9-2.Under illumination,the Fe2+ concentration in both aseptic and dead bacteria groups increased,sufficiently demonstrating the reduction of Fe3+ by light,and the Fe2+ concentration in the dead bacteria group increased more than that in the aseptic group,indicating that the participation of organic matter in the sterile group made the reduction of Fe3+stronger than that of the aseptic group.In addition,the growth of AMDY2-9-2 was accelerated under illumination,the logarithmic growth period was earlier and the growth amount increased,which indicated that illumination promoted the growth of iron-reducing bacteria themselves.In the study of the effect of light on iron oxidation,three groups of experiments were designed:including viable bacteria group,dead bacteria group and aseptic group.Each group was divided into light and non-light conditions.The growth period,pH,Eh,Fe2+,Fe3+ concentration and other parameters under or without light were studied with W-4-3.In the aseptic group and the dead group,photooxidation dominated,while in the living bacteria group,under light conditions,Fe3+ could interact with the organic substances secreted by the iron oxidizing bacteria W-4-3,and Fe3+ was reduced to Fe2+ through LMCT reaction,and the photoreduction effect was greater than the photo-induced chemical oxidation.The continuous regeneration of Fe2+ by photoreduction will promote the growth of W-4-3,and the increase of W-4-3 will lead to more Fe2+being oxidized.Generally,the overall performance of this experiment is that light promotes ferric oxidation by W-4-3.The proteomic study of AMDY2-9-2 and W-4-3 was divided into experimental group and control group with iTRAQ and LC-MS/MS technology.The experimental group had light conditions,while the control group had no light conditions.The experimental group and the control group had both three parallel conditions.295 differentially expressed proteins were screened in AMDY2-9-2,of which 132 proteins were up-regulated and 163 proteins were down-regulated.515 differentially expressed proteins were screened in W-4-3,of which 237 proteins were up-regulated and 278 proteins were down-regulated.However,GO enrichment analysis showed that growth-related proteins were differentially expressed,and no significant difference was detected for iron redox-related proteins.Therefore,it is believed that light mainly promotes the growth of microorganisms,and has less impact on the functions of iron reducing bacteria and iron oxidizing bacteria. |
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