Removal Of Microcystin-LR By Probiotics: Screening And Mechanism Analysis

Microcystins, a kind of cyclic heptapeptide produced by cyanobacteria, are regarded as hepatotoxins and tumor promoters. In this case, removing cyanobacterial toxins plays an important role in the area of food security and environmental control.In this study, 33 strains of lactic acid bacteria isolated from many sorts of traditionally fermented pickles or sausages were identified, and their abilities to remove the cyanobacterial peptide toxin microcystin-LR(MC-LR) in aqueous solutions were assessed. Among them, the strain BBE10-212 showed the hightest efficiency in toxin removal, and was classified phenotypically as a member of the genus Lactobacillus casei on the basis of 16S rDNA sequencing. Meanwhile, bacterial concentration, MC-LR concentration, cells viability and metabolic activity make impact on the removal of MC-LR. In addition, A maximum removal of 52 % was observed for BBE10-212 with 5 % glucose supplementation compared with 19 % removal in PBS alone. However, the existence of some inorganic nitrogen as nitrogen substitute of MC-LR and certain metal ions as key metabolic co-enzymes reduced the removal efficiency of the tested strain.To better understand the response of the tested strain to the presence of MC-LR, two-dimensional gel electrophoresis was used to investigate which proteins are changed in the presence of MC-LR. Fifteen identified proteins were changed in the presence of MC-LR. The relative intensity of 7 protein spots was at least twofold higher in the presence of MC-LR than in its absence, whereas the relative intensity of 8 protein spots was half that under the same condition. Most differentially expressed proteins were downregulated in the presence of MC-LR participate in glycolysis. This suggests that the carbohydrate metabolism of L. casei is impaired when tested strain is exposed to MC-LR. On the other hand, mannitol was produced in the presence of MC-LR. Mannitol has been reported to accumulate in response to environmental oxidative damage by oxygen radicals. We presume that the accumulation of mannitol protects L. casei against oxygen stress, which produced by MC-LR.The result of the study supplies a novel way to understand the removal mechanism of MC-LR. Moreover, it enlightens us to improve the removal efficiency of MC-LR with more strategies based on the metabolic control of strains.