| Bacillus megaterium is a common soil bacterium.Studies have shown that inoculation with exogenous Bacillus megaterium can effectively increase the bioavailability of heavy metals in contaminated soil,and then activate soil heavy metals.At the same time,the growth and metabolism of Bacillus megaterium are regulated by both nutrient and growth conditions,which indirectly affects its activation of soil heavy metals.However,there are few studies about the optimization of Bacillus megaterium nutrient and its effects on the bioavailability of heavy metals in mining soils;especially using Bacillus megaterium on the bioavailability of Pb,Zn,and Cd in soils of lead-zinc mines in the dry and hot valley of the Southwest Sichuan have not been reported.Therefore,this study investigated the effects of growth-related substances on the activation of Pb,Zn,and Cd in the soil of the Pb-Zn mine in Ganluo County by Bacillus megaterium,with the purpose of:(1)screening out nutrient conditions that could significantly promote the activation of Pb,Zn and Cd in the soil by Bacillus megaterium;(2)Providing theoretical support and technical guidance for the activation of heavy metals in the soil of Ganluo Pb-Zn mine.The results are as follows:(1)In the period of 0-50 days,the content of Pb,Zn,Cd in the weak acid extractable state of mine soil could be increased by inoculating Bacillus megaterium,which cultured in A,B,C,D medium,respectively.Among them,inoculation with Bacillus megaterium cultured in D medium could significantly increase the content of weakly acid extractable Pb,Zn,and Cd in the soil,and also significantly reduce the content of residual Pb,Zn,and Cd in the mine soil.At the same time,it could also significantly reduce the pH of mine soil,and improved the content of alkali hydrolyzed nitrogen and available phosphorus.Therefore,D medium is the most effective medium among the four basic media to promote the activation of Pb,Zn and Cd in the soil of Ganluo Pb-Zn mine by Bacillus megaterium.(2)Based on the D basic medium,four different optimised mediums of J1,J2,J3,and J4 were designed here,which have different carbon-nitrogen ratio as follow 5:1,10:1,20:1,and 40:1,respectively.Then they were used to culture Bacillus megaterium,and then the cultured bacteria were inoculated in the soil of Ganluo lead-zinc mine.The results showed that: in 0-35 days,inoculation of Bacillus megaterium fermentation broth J1,J2 and J3 could significantly increase the contents of weak acid extractable Pb,Zn and Cd in mine soil.Meanwhile,the average biological activity coefficients of Pb,Zn and Cd in 0-50 days were as follows: Pb: J2(20.87%),J1(20.67%),J3(20.39%);Zn: J3(28.18%),J1(28.11%),J2(27.28%);Cd: J2(50.63%),J1(49.99%),J3(49.97%).Based on the biological activity coefficient,J1 can more effectively and equably activate Pb,Zn and Cd in mine soil.In addition,J1 treatment could not only increase the contents of available potassium and available phosphorus in mine soil,but also significantly reduce the pH of mine soil by 0.17.Therefore,the optimized J1 medium is the most suitable medium for Bacillus megaterium to activate Pb,Zn and Cd in mine soil.(3)Based on the J1 medium,four different treatments of J1-0,J1-5,J1-10 and J1-20 were designed with supplementary dosage of 0 ml,5 ml,10 ml and 20 ml,respectively.The results show that: at 0-35 days,the treatments of J1-0,J1-5 and J1-10 could significantly promote the activation of Pb,Zn and Cd in mine soil by Bacillus megaterium,while the treatments of J1-20 was completely opposite to the treatments of J1-0,J1-5 and J1-10.Among them,the treatment of J1-5 had the best effect on increasing the content of weak acid extractable Pb in mine soil,its average increase was 42.19 mg/kg.On the other hand,the treatment with the highest average weak acid extractable Zn content was J1-10,its average weak acid extractable Zn content was about 603.51 mg/kg.However,the treatments of J1-0,J1-5 and J1-10 had the same effect on the increase of weak acid extractable Cd content.In addition,the treatments of J1-0,J1-5 and J1-10 could also significantly reduce the pH of mine soil and increase the content of a vailable phosphorus and available potassium in the soil.Based on the biological activity coefficient,between20-50 days,the average Pb and Zn biological activity coefficients of J1-5 and J1-10 treatments were basically the same,and they were greater tha n J1-0.The results showed that 5 ml or 10 ml medium could enhance the activation effect of Bacillus megaterium on Pb and Zn in mine soil.Taking into account the cost control,5 ml was selected as the best supplement quantity.Therefore,in this article,the biological activity of Bacillus megaterium was improved by optimizing its nutrients.As a result,the weak acid extractable state of Pb,Zn and Cd in mine soil can be effectively improved,and the soil Pb,Zn and Cd,can be activated.In order to further realize the technical system of co-activation of Pb,Zn,Cd in the soil of Ganluo Pb-Zn mine by N utrient-Bacillus megaterium,a quite effective construction was constructed. |
