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Study On Isolation,Identification,Adsorption Characteristics And Mechanism Of Lead-resistant Lactic Acid Bacteria

Posted on:2020-04-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:X F ZhaoFull Text:PDF
GTID:1360330578956501Subject:Food Science
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Lead is a heavy metal element with strong accumulation.In the presence of trace amounts,it can also cause great harm to the human body.The United Nations Environment Programme ranked that the lead is the second hazard,because it has strong cumulativity and reversibility.Lead pollution have been frequently reported as a hazard to human health in recent years.More and more attention has been paid to the pollution of lead.Traditional physical and chemical methods for the removal of heavy metals have some defect such as high cost and large side effects.But the biosorption method has been widely concerned because of its high efficiency and no secon dary pollution.Previous reports have demonstrated that Lactic acid bacteria(LAB)has ability to absorb heavy metal lead,so the use of food-grade LAB to treat heavy metal pollution has become a new research field.In this paper,twenty-three soil samples contaminated with heavy metal were collected from Baotou Baogang Mining Area and Baiyun Obo Iron Mine.The 104 LAB strains were isolated from the above soil by using the method of dilution plate.The 10 strains of LAB with high tolerance of lead were identified by morphological characteristics analysis,physiological and biochemical identification and 16S rRNA sequence analysis.The result showed that the strain of Qac,Qad,Qae,Kd42 were Lactobacillus plantarum,the strain of Fe3 and lOal were Pediococcus pentosaceus,the strainof Qaa was Enterococcus hirae,the strain of Qab was Lactobacillus sakei,the strain of Haa and Qal 1 were Weissella cibaria.E.hirae Qaa and P.pentosaceus Fe3 strain were selected as high lead adsorption strains from the above 10 strains based on the adsorption rate.The adsorption rates of the E.irae Qaa and P.pentosaceus Fe3 strains were 58.73±1.05%,90.10±0.36%,respectively.E.hirae Qaa and P.pentosaceus Fe3 strains were used in the lead adsorption experiments which were conducted to investigate the effects of factors pH,lead initial ion concentration,adsorption time,adsorption temperature and cell concentration on lead adsorption efficiency.The optimal adsorption condition of two strains were explored by response surface method.The optimal adsorption conditions of E.hirae Qaa adsorption lead were obtained with 8.24mg/g at adsorption time was 230min,wet cell concentration was 6g/L,Pb2+concentration was 80 mg/L,pH value was 5.6.The optimal adsorption conditions of P.pentosaceus Fe3 adsorption lead were obtained with 19.79mg/g at adsorption time was 246min,wet cell concentration was 4.18g/L,Pb2+ concentration was 85.26mg/L,pH value was 5.11.At the same time,Langmuir and Freundlich isothermal adsorption models and quasi-secondary adsorption Kinetics equations were used.The adsorption process of Pb2+ by E.hirae Qaa and P.pentosaceus Fe3 did not conform to Freundlich isothermal adsorption model.But all conform to Langmuir isothermal adsoption model and Quasi-second-order adsorption kinetic equation.The results of scanning electron microscope(SEM)showed that the surface of cells become deformation,depression,adhesion,even rupture,and sediments gathered on the surface after the adsorbing of Pb2+.While the transmission electron microscope(TEM)images presented that lead deposits could be observed within the cells.Energy dispersive spectroscopy(EDS)showed that there was lead inside the bacteria,indicating that the bacteria not only have surface adsorption,but also include intracellular accumulation.The result of Fourier Transform Infrared Spectrum(FT-IRF)showed hydroxyl(O-H),amide(N-H)andcarboxyl(C=O)groups were involved in biosorption process.The complexation,ion exchange,electrostatic interaction and intracellular diffusion were the main mechanisms of E.hirae Qaa ?Rpentosaceus Fe3 adsorbing Pb2+.Nucleic acid,phosphate,polysaccharide and S-layer protein and fatty acids also participated in the adsorption process.After the carboxyl groups,hydroxyl groups,amino groups and other functional groups on the bacterial cells were masked with different chemical reagents,the adsorption effect of the two test strains was significantly reduced.It showed that these functional groups played an important role in the process of adsorption of Pb2+.Desorption of lead by different desorbents results showed that 0.1mol/L HCl had the best desorption effect.The adsorption capacity of two inactivated test strains to Pb2+ decreased by half.While the Pb2+ adsorption capacity of strains was improved obviously after the NaOH treatment.
Keywords/Search Tags:Lactic acid bacteria(LAB), Lead, Identification, Adsorption characteristic, Adsorption mechanism
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