| Heavy metal pollution has been one of the most difficult problems to deal with.Industries,agriculture and mining lead to a large number of heavy metal emissions which have seriously threatened to ecological environment and people's health.Bioremediation has the advantages of low ecological risk and cost.However,the phytoremediation method suitable for large-scale application has many disadvantages such as long cycle,low biomass and easy to environmental impact.Therefore,it is necessary to find a more efficient and environmentally friendly remediation method for heavy metal pollution.Microorganisms have stronger adaptability and faster growth rate than plants.Moreover,efficient adsorption materials can further enhance the efficiency of microbial remediation.Therefore,in this paper,in order to find a new strategy for bioremediation,mushroom mycelium was selected for bioremediation,and the repair effect was enhanced by adding graphene oxide(GO).Firstly,Lead-tolerant mushroom was found by plate screening.At the same time,the influences of GO on the lead tolerance of mycelium were studied.Secondly,the potential ecological risks of GO application were evaluated.Thirdly,GO was used to strengthen the repair effect of mycelium on soil lead pollution.Furthermore,the mechanisms of GO promoting mycelium growth and strengthening mycelium enrichment under lead stress were preliminarily discussed by simulation experiment in water.The main conclusions are as follows:(1)The plate screening method was used by adding different concentrations of lead solution.The growth of various mushroom mycelium was observed.The results show that the lead-tolerance of Morchella sextelata was best,and the growth of M.sextelata was fastest.Under the stress of 350 mg/L lead,the growth rate was 23.93 mm/d.M.sextelata is a bioremediation strains with enormous potential utilization value.In addition,on the basis of this experiment,the effect of GO on the M.sextelata leadtolerant was studied by adding GO.The results showed that under the lead stress of 350mg/L,the inhibition rate of mycelia growth decreased by 2.37% after culture for 3 days which indicating that GO has a certain shielding effect on the lead stress.(2)The liquid fermentation method was used to research the potential risk of GO application.The toxicity of GO to the M.sextelata and the effects of M.sextelata to GO were studied by Adding different GO concentrations in liquid medium.The results show that GO can promote the growth of M.sextelata mycelium below the 50 mg/L.inhibited the growth of M.sextelata mycelium when the GO concentration reached 100 mg/L.mycelial dry weight increased by 12.38% under 10 mg/L GO.The mycelial dry weight was reduced by 10.10%,when the GO concentration increased to 200 mg/L.The toxic action mechanism of GO on mycelia is mainly that GO can cover the surface of mycelia which lead the exchange of substances between mycelia and the environment to be difficult.meanwhile,the malondialdehyde(MDA)content in mycelia cells is increased.In addition,the nitrogen content of GO increased by up to 4.28% and the oxygen content decreased by up to 9.42% after mycelia treatment.Moreover,the dispersion in ethanol decreased.Those phenomenons indicate that the mycelia caused the deoxygenation,nitrogen-dopant and introduce more defective structures in GO.(3)The remediation effects of M.sextelata mycelium to lead contamination soil were studied by inoculation M.sextelata.Under circumstances of the Pb addition by 50 mg/kg,250 mg/kg,500 mg/kg and 800 mg/kg,the plant restoration made the biomass of alfalfa grass increase by 4.46%,13.50%,19.90% and 9.64%,respectively,and M.sextelata mycelium restoration made the biomass increase by 90.47%,113.31%,95.10% and 134.00%,respectively.At the same time,in the M.sextelata mycelium and GO restoration group,the biomass increased by 108.47%,145.71%,139.24% and 208.60%,respectively.The results indicated that the method of GO and M.sextelata mycelium collaborative restoration was more effective.Moreover,the content of bioavailable lead was biggest decreased by 76.51% after the repair by mycelium and GO.The main repair effect of mycelium on soil heavy metal pollution is biological fixation.(4)In order to further explore the fixation effect of mycelium on lead and the synergistic mechanism of GO,M.sextelata were inoculated into the medium containing different concentrations of lead.The influence of GO on the growth and lead adsorption characteristics of M.sextelata mycelium under lead stress was studied.The results showed that the presence of GO reduced the toxic effect of lead on mycelia which lead the dry weight of mycelia increased by 65.33%.At the same time,GO significantly promoted the adsorption and lead fixation on M.sextelata mycelium.After the synergistic effect of GO and mycelium,the removal rate of lead in the medium was up to 88.41%.SEM and FT-IR showed that the enrichment of lead by mycelium was mainly realized by surface adsorption and extracellular fixation. |
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