| Hexavalent chromium [Cr(VI)] is a priority heavy metal pollutant causing a series of environmental issues,and bio-reduction of Cr(VI)to trivalent chromium can remarkably decrease the environmental risk of Cr(VI).The reduction and resistance abilities of microorganisms to Cr(VI)can be dramatically improved by acclimatization.The exploration of key proteins or biological processes affected by environmental stress through proteomics techniques has received increasing attention.In this study,Cr(VI)was selected as the target pollutant to carry out microbial acclimatization and omics researches.The findings of this study present novel insights into the molecular mechanisms for the reduction and resistance and its performance stability of Shewanella oneidensis MR-1 responding to long-term Cr(VI)stress at the proteome level,which could help us to make effective bioremediation and environmental risk assessments through long-term acclimatization.In order to provide certain reference for the prevention and treatment of environmental pollution.Based on this,the specific work of this study is as follows:On one hand,we collected S.oneidensis MR-1 from a 120-day acclimatization by increasing Cr(VI)concentration in the culture media to investigate its adaptation mechanisms under long-term Cr(VI)stress at the proteome level.First,the Cr(VI)reduction capacity,morphology and electrochemical characteristics of S.oneidensis MR-1 were studied.The results showed that long-term Cr(VI)acclimation could improve the reduction and tolerance of S.oneidensis MR-1 to Cr(VI).Through a scanning electron microscope(SEM)it was observed that morphological changes were made to adapt to the stress environment.sivatensis also changed,and differential pulse voltammetry(DPV)data showed that the characteristic peaks of electrochemical also changed.Then,tandem mass tag-based(TMT)quantitative proteomic analysis was performed to study the differences between 9 collected samples.A total of 2500 proteins were quantified from 2723 identified protein groups.Based on the above data,we carried out a systematic bioinformatics analysis of the quantifiable proteins,including protein annotation,function classification,function enrichment and enrichment-based clustering analysis.A quantitative ratio of higher than 2 was considered to be an upregulation,whereas that less than 0.5 was considered to be a downregulation,and P <0.05.There were 239,509 and 447 differentially expressed proteins in three comparison groups respectively,namely D120Cr(-)/D120 N,D120Cr(+)/D120 N and D120Cr(+)/D120Cr(-).Bioinformatics analysis showed that the differentially expressed proteins after the 120-day Cr(VI)acclimatization were mostly related to flagellar assembly,ribosomes,transport,efflux,sulfur metabolism,iron acquisition and homeostasis,and energy metabolism.The reduction capacity of S.oneidensis MR-1 to Cr(VI)was enhanced mainly in electron transport systems and energy metabolism.The resistance capacity to Cr(VI)was promoted mainly in cellular motility,efflux systems,sulfate transport,sulfur metabolism,oxidative stress protection and energy metabolism.The Cr(VI)reduction was carried out by intracellular and extracellular reduction.The Cr(VI)resistance was mainly in uptake,efflux,antioxidant and repair systems.On the other hand,D120 Cr was cultured for 120 days in 300 mg/L Cr(VI)and normal environment for 60 days to study the stability of Cr(VI)reduction ability and tolerance and its internal mechanism.The reduction ability of hexavalent chromium was determined,and it was found that the strains cultured under normal environment and stress environment had good reduction and tolerance ability to Cr(VI).It was found by scanning electron microscopy that the morphology of the strains was changed under Cr(VI)stress.Then,through Lable-free quantitative proteomics technology,the difference analysis of Cr(VI)stress response of 9 samples before and after culture in different environments was carried out.A total of 2179 proteins were identified,of which 2146 were quantified.Differentially expressed proteins were screened according to a quantitative ratio of higher than 2 was considered to be an upregulation,whereas that less than 0.5 was considered to be a downregulation and P <0.05,and subsequent bioinformatics analysis was conducted together with the differentially expressed proteins in one group of samples with two or more times of non-null values and the other group with all data of null values.There were 212,459 and 219 differentially expressed proteins in the three comparison groups of D180N/D120 Cr,D180Cr/D120 Cr and D180N/D180 Cr,respectively.GO function and KEGG pathway annotation results showed the functions and biological processes of differentially expressed proteins in all comparison groups are very similar.The functions mainly involved catalytic activity,binding,transporter activity,transcription regulator activity and structural molecule activity.It is mainly involved in important biological processes such as cellular process,metabolic process,biological regulation,response to stimulus,localization and regulation of biological process,ect.The GO enrichment results showed that the response differences between the strains to high concentration of Cr(VI)stress were mainly manifested in important biological processes such as sulfate assimilation,hydrogen sulfide metabolic process,toxin biosynthetic process,organonitrogen compound catabolic process,amino acid catabolic process,cysteine biosynthetic process,formate or formamide metabolism and imidazole-containing compound catabolic process,ect.The KEGG pathway enrichment analysis showed that the response differences of the strains to Cr(VI)were mainly reflected in the important metabolic pathways of pentose and glucuronate interconversions,beta-Lactam resistance,cysteine and methionine metabolism,cationic antimicrobial peptide(CAMP)resistance and sulfur metabolism,among which the sulfur metabolism pathway was particularly important. |
PDF Full Text Request