Study On The Removal And Mechanism Of Microcystin-lr By Probiotics

Aimed at the problem of microcystin-comtaminated in water and food existed extensively, in this paper, probiotics were used as the research objects. Nine strains, (such as L. salivarius BBE09-18, L. delbrueckii subsp FBC07-47, L. fermentum BBE09-29, L. bulgaricus FBC08-03, L. helveticus FBC08-15, and L. casei Zhang etc), were evaluated for their capability of microcystin-removal. Feasibility analysis of microcystin removed by probiotics was carried out, and screened the strains possessed high capability of microcystin-removal. The key factors related to the removal efficiency and the possible removal-mechanisms were also investigated in this paper. The main results of this dissertation were described as follows:1. Nine probiotic bacterias commonly used in food industry were selected as research subjects, and were investigated the feasibility of MC-LR removed by probiotics. The results showed that, all of the nine tested strains are possessed the capability of microcystin-removal, but the efficiency of MC-LR removal was significantly different between genera. Among these tested strains, L. casei Zhang exhibited the highest removal efficiency. After a removal treatment with L. casei Zhang for 24 h (109 CFU/mL, pH 7.0, 37°C), the MC-LR concentration reduced from 150μg/L to 85.5μg/L, and the clearance rate was up to 43%.2. On the basis of the feasibility study of MC-removal by probiotics, L. casei Zhang, L. fermentum BBE09-29 and L. salivarius BBE09-18 were selected from the tested strain according to the eliminate efficiency, and were used to research the key factors related to the removal efficiency. The results indicated that, various parameters, such as biomass, temperature, toxin concentration and cytoactive, were found to played important roles on the MC-LR removed by probiotics; In addition,the physiological status of cells have an important influence on microcystin-removal, the viable cells were more effective for MC-LR removal than the nonviable ones.3. In the further study, carbon and nitrogen sources were added into the compound system of strain and microcystin-LR, the changes of MC-LR removal, viable cells and total protease activity of probiotics were investigated after the probiotic cells activity regulation. The results showed, the removal performance can be improved significantly with the supplement of carbon source, and the intracellular total protease activity was also been improved. But this phenomenon wasn't happened while the nitrogen sources were added.4. In order to investigate the pathway and mechanism of MC-LR removed by probotics, changes of the whole-cell protein and MC-LR concentration in extracellular and intracellular systems were investigated. The effectiveness of microcystin-LR removal by viable cells, nonviable cells and cell-free extract were compared. LC-MS was being used to analyse the metabolites change in complex system of strain and microcystin. The results showed that three middle-molecular weight protein band appeared in cells after probiotics induced by MC-LR, and may be relevant with the degradation of MC-LR; The CFE possessed the ability of MC-LR degradation, and which confirmed the performance of microcystin removed by probiotics was related with biodegradation.