Biosorption Mechanism Of Heavy Metals By Bacillus Cereus RC-1: Ion Exchange

With the rapid economic development,environmental problems such as heavy metal pollution in water and soil have become serious.In recent years,many scholars put forward in view of the method of microbial remediation in heavy metal pollution due to its advantages of low cost and no secondary pollution,and it has a good application prospect.Investigation on the detoxification mechanism of heavy metals by microbial cells will provide theoretical foundation and scientific basis for microbial remediation and it is important practical significance to improve the quality and safety of agricultural products,and protect human health.This study selects B.cereus RC-1 which is resistance to heavy metals as research object,microorganism heavy metal experiments were conducted to study the biosorption characteristics of heavy metals Cd,Cu,Zn and Pb in different conditions and explore the biosorption mechanisms by means of SEM-EDS,TEM,FTIR.Finally,the physiological detoxification mechanism of B.cereus was studied by using trace elements and cationic release experiments under metals stress.The results show that:?1?B.cereus RC-1 is resistant to heavy metal Cd,Cu,Zn,Pb,including the strongest resistance to Cd with the minimum inhibitory concentration of 400 mg/L,and the resistance for Cu is the worst,only 80 mg/L.The optimum biosorption condition of 4 heavy metals by B.cereus RC-1 are 180 r/min,30?,pH=7?Cd?;150 r/min,40?,pH=7?Cu?;180 r/min,30?,pH=7?Zn?;120 r/min,30?,pH=7?Pb?.In addition,OD₆₀₀,removal rate with the incubation time increased slowly at the beginning,then showed a trend of sharp increase,and finally back into balance.While pH decreased at first and rose later.?2?SEM-EDS analysis found that,compared with normal cell,there is rough surface with crystal particles containing heavy metal ions of Cd,Cu,Zn,and Pb treatment.In addition,Cd,Cu,Zn,and Pb treated cells also change significantly,there are rough edges,visible electronic particles with high density and the cellular structure is damaged.Compared to CK treatment,the infrared spectrum peak position offset,wave increased for Cd,Cu,Zn and Pb treatment.The main changes of functional groups of Cd,Cu treatment are C=O,-CH,-CN,-CO,C-I,-OH,-NH,C=O,-CH for Zn treatment,and C=O,-CH,C-I for Pb treatment.Trace element analysis showed that bio-enzymes related to Fe,Cu,Mn,Co,Se,Zn,Ni,Mo of B.cereus RC-1 had changed,these enzymes play an important role in the heavy metals detoxification,mainly including oxidase?Cd,Cu,Zn,Pb?,hydrocarbon transfer of enzyme?Cd,Zn?and methyl reductase?Cu,Pb?.?3?B.cereus RC-1 ion exchange experiment with Cd,Cu,Zn and Pb were conducted based on initial concentration of heavy metals,culture time and nutrient solution pH.The results show that K⁺,Ca²⁺,Mg²⁺are involved in ion exchange of B.cereus RC-1 for Cd stress,K⁺,Ca²⁺,Mg²⁺,Na⁺for Cu,Zn treatments,Na⁺,K⁺,Ca²⁺for Pb treatment under Pb²⁺stress.When exposed to Cd²⁺concentration of 100 mg/L,release quantity of K⁺,Ca²⁺,Mg²⁺are the biggest with 0.56mmol/L,showing the order as:K⁺>Ca²⁺>Mg²⁺.Similarly,as Cu²⁺concentration of 20 mg/L,K⁺,Ca²⁺,Mg²⁺,Na⁺release a quantity to maximum,4.34mmol/L,with the order as:Na⁺>K⁺>Mg²⁺>Ca²⁺.As Zn²⁺concentration of 100 mg/L,K⁺,Ca²⁺,Mg²⁺,Na⁺release quantity are the biggest,the total release reach 5.54 mmol/L,with the order as:Na⁺>K⁺>Mg²⁺>Ca²⁺.As Pb²⁺concentration of 120 mg/L,Na⁺,K⁺,Ca²⁺total release is the largest,3.93mmol/L,with the order as:Na⁺>K⁺>Ca²⁺.The total release quantity?0.66mmol/L?of K⁺,Ca²⁺,Mg²⁺in the solution reach balance after 20 hours of RC-1 with Cd²⁺,with the biosorption of 0.062mmol/L Cd²⁺.The total cationic release quantity with Cu²⁺,Zn²⁺,Pb²⁺reach balance after 24 hours,the total release of Cu treatment achieve 3.10 mmol/L with the biosorption of 0.13 mmol/L Cu²⁺;Zn²⁺release 0.74 mmol/L with the biosorption of 0.38mmol/L Zn²⁺;Total release quantity is 2.55 mmol/L of Pb treatment,with the biosorption of 0.16 mmol/L Pb²⁺.When pH is 7,the total cationic release quantity reach the maximum of Cd,Cu,Pb treatment,including K⁺,Ca²⁺,Mg²⁺total release quantity of 0.23mmol/L for Cd treatment,removing 0.069 mmol/L Cd²⁺;K⁺,Ca²⁺,Na⁺,Mg²⁺total release quantity reach 1.75mmol/L for Cu treatment,removing 0.10mmol/L Cu²⁺;K⁺,Ca²⁺,Na⁺total release quantity reach 1.27mmol/L for Pb treatment,removing 0.15 mmol/L Pb²⁺.When the pH is 6,K⁺,Ca²⁺,Na⁺,Mg²⁺maximum total release quantity reach 3.44 mmol/L for Zn treatment,removing 0.28 mmol/L Zn²⁺.