Study On The Mechanism Of Cadmium Biosorption By Lactic Acid Bacteria

Cadmium is a typical heavy metal pollutant,which is easy to migrate into the food chain and endanger human health.Because of its strong toxicity and easy to accumulate,etc.,so it was named as a class I carcinogen by the international cancer research center.Biosorption technology is an effective means to remove water and other liquid cadmium in food,and the lactic acid bacteria has the advantages of low cost,abundant resources,strong adsorption,high security and other advantages,has important advantages in this aspect.In this study,23 strains of lactic acid bacteria were used as the tested strains,and the adsorption capacity,influencing factors and mechanism were studied.(1)Respectively under the condition of pH 4,5,6 and 7,23 strains of inactived lactic acid bacteria for the adsorption ability of cadmium was studied.The adsorption ability of lactic acid bacteria depends on pH,with the increase of pH the adsorption capacity of cadmium increased significantly.Under the condition of pH 4,the adsor:ption capacity of most of lactobacillus is none,and only 3 strains showed the adsorption capacity,the adsorption rate of cadmium is in the range of 9.2%-35.2%,and the adsorption ability of lactococcus lactis is great,the adsorption rate is in the range of 3.7%,29.1%;At pH 7,the adsorption capacity of lactic acid bacteria on cadmium reached the highest.The adsorption rate of lactobacillus on cadmium is 45.2%-81.7%,the adsorption rate of lactococcus lactis on cadmium is 66%-92.1%.Lactococcus lactis adsorption rate of cadmium is generally larger than that of Lactobacillus,at pH 7,Enterococcus devriesei HLJ 15005 adsorption rate of cadmium reached 92.1%.(2)Respectively select two strains from lactobacillus and lactococcus lactis for the further study.Carbolfuchsin staining test showed that 4 strains of lactic acid bacteria cell surface had no capsular structure test;denaturing polyacrylamide gel electrophoresis showed that only Lactobacillus acidophilus NCFM contains S cell surface layer protein structure for the 4 strains of lactic acid bacteria,and its molecular weight is 46 kDa.Further experiments showed that in the process of adsorption of cadmium the S protein in strain NCFM not only did not play a key role,but inhibited the adsorption ability of strain NCFM on Cd2+,removing the S layer protein of strain NCFM by 5 mol/L lithium chloride solution,then the adsorption ability of strains of cadmium increased significantly,increased by 14.5%.(3)The key components of the surface of lactic acid bacteria cells were treated by chemical removal and chemical modification.The results showed that the peptidoglycan on the cell wall of inactivated lactic acid bacteria played a key role in the adsorption of cadmium.By Fourier transform infrared spectroscopy technology of lactic acid bacteria groups on the adsorption of cadmium was analyzed.As usual at the peak of 3294.3 cm-1,1531.4 cm-1,1386.7 cm-1,1234.4 cm-1 and 1070.4 cm-1 shifted after the adsorption cadmium,suggesting that cell surface active groups,amino,hydroxyl and carboxyl groups are the key to the adsorption of cadmium.