Fermentation Of Aflatoxin-inhibiting Deep-sea Bacteria And Characterization Of Bioactive Metabolites

The deep-sea area, an area in which humans rarely get involved, contains extremely rich microbial resources. Nowadays, exploitation of ocean resources becomes increasingly important. As more and more crops and animals are being contaminated by mycotoxin, such as aflatoxin, it might be a promising biological prevention method to find microorganisms in deep-sea area to inhibit Aflatoxin’s toxicity.To find an efficient and environment friendly method of inhibiting Aflatoxin’s toxicity, optimization of deep-sea bacteria fermentation conditions was searched to obtain active materials.In this thesis, visualizing screening plate method was used to provide strains with activities of inhibiting Aflatoxin’s toxicity, and 149 strains bacteria were obtained. About 29.50% of total strains of bacteria, 44 strains with high activity were screened using tip-culture method, which had 80% inhibition rate. 14 strains of bacteria could completely inhibit Aflatoxin’s toxicity, accounting for 9.40% of total strains and 31.80% of the total high activity strains. The p H of 79 strains’ fermentation liquid was alkaline(p H 8-9), accounting for 53.02% of the total strains; 26 were neutral(p H 7), accounting for 17.45% of the total strains; and 44 were acidic, accounting for 29.53% of the total strains.The optimal separate fermentation medium for a part of bacteria strains with high activity was screened from five types of medium, which were A1, starch casein, PDA, ISP2, and actinomycetes culture medium. The environmental factors in fermentation and nutrition components in medium of FA13 were verified via the method of uniform design, and then the optimal combination was determined: yeast extract powder 9.3690 g/L, malt extract 2.0820g/L, glucose 13.860g/L, inoculation quantity 1.061%, culture temperature 21℃, culture time 10 d, p H 6.2. The rates of inhibiting bacteria and toxicity of this solution were 7.2 and 1.6 times higher than the previous one, separately.In this thesis, characteristics of temperature stability, p H stability and enzymolysis stability of fermentation liquid of FA13, ZL3, 13-1T, strains with high activity, on the corresponding optimal medium were studied. The results showed that, ISP2 medium fermentation liquid of FA13 was stable to temperature, acid-base and enzymolysis; starch casein fermentation liquid of ZL3 was unstable to temperature, acid-base and enzymolysis; ISP2 medium fermentation liquid of 13-1T was stable to temperature and acid-base, but not stable to enzymolysis; starch casein fermentation liquid of FA13 was stable to temperature and enzymolysis, but showed unstable in alkali environment. In addition, starch casein and ISP2 fermentation liquids of FA13 were stored for 6 months at room temperature had no change in their rates of inhibition of bacteria and toxicity. The characteristic of anti-bacteria and anti-toxicity of active materials extracts of FA13 in optimized fermentation liquid in four organic solvents including n-butyl alcohol, ethyl acetate, chloroform and petroleum were detected, and the results showed that, n-butanol extract had the best inhibition effect while the extract effect of ethyl acetate was the worst.