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Biological Degradation of Aflatoxin B₁ by Cell-Free Extracts of Bacillus velezensis DY3108 with Broad PH Stability and Excellent Thermostability.

ABSTRACT: (1) Background: Aflatoxin contamination in food and grain poses serious problems both for economic development and public health protection, thus leading to a focus on an effective approach to control it; (2) Methods: Aflatoxin B₁ (AFB₁) degrading bacteria were isolated using a medium containing coumarin as the sole carbon source, and the biodegradation of AFB₁ by the isolate was examined by high performance liquid chromatography, and liquid chromatography mass spectrometry; (3) Results: a bacterial strain exhibiting strong AFB1 degradation activity (91.5%) was isolated and identified as Bacillusvelezensis DY3108. The AFB₁ degrading activity was predominantly attributed to the cell-free supernatant of strain DY3108. Besides, it was heat-stable and resistant to proteinase K treatment but sensitive to sodium dodecyl sulfate treatment. The optimal temperature for the maximal degradation of AFB₁ was 80 °C. Even more notable, the supernatant showed a high level of activity over a broad pH (4.0 to 11.0) and exhibited the highest degradation (94.70%) at pH 8.0. Cytotoxicity assays indicated that the degradation products displayed significantly (p < 0.05) lower cytotoxic effects than the parent AFB₁; (4) Conclusions: B.velezensis DY3108 might be a promising candidate for exploitation in AFB₁ detoxification and bioremediation in food and feed matrices.

SUBMITTER: Shu X

PROVIDER: S-EPMC6116002 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Thermostable T1 lipase from Geobacillus zalihae has been crystallized using counter-diffusion method under space and Earth conditions. The comparison of the three-dimensional structures from both crystallized proteins show differences in the formation of hydrogen bond and ion interactions. Hydrogen bond and ion interaction are important in the stabilization of protein structure towards extreme temperature and organic solvents. In this study, the differences of hydrogen bond interactions at position Asp43, Thr118, Glu250, and Asn304 and ion interaction at position Glu226 was chosen to imitate space-grown crystal structure, and the impact of these combined interactions in T1 lipase-mutated structure was studied. Using space-grown T1 lipase structure as a reference, subsequent simultaneous mutation D43E, T118N, E226D, E250L, and N304E was performed on recombinant wild-type T1 lipase (wt-HT1) to generate a quintuple mutant term as 5M mutant lipase. This mutant lipase shared similar characteristics to its wild-type in terms of optimal pH and temperature. The stability of mutant 5M lipase improved significantly in acidic and alkaline pH as compared to wt-HT1. 5M lipase was highly stable in organic solvents such as dimethyl sulfoxide (DMSO), methanol, and n-hexane compared to wt-HT1. Both wild-type and mutant lipases were found highly activated in calcium as compared to other metal ions due to the presence of calcium-binding site for thermostability. The presence of calcium prolonged the half-life of mutant 5M and wt-HT1, and at the same time increased their melting temperature (Tm). The melting temperature of 5M and wt-HT1 lipases increased at 8.4 and 12.1 °C, respectively, in the presence of calcium as compared to those without. Calcium enhanced the stability of mutant 5M in 25% (v/v) DMSO, n-hexane, and n-heptane. The lipase activity of wt-HT1 also increased in 25% (v/v) ethanol, methanol, acetonitrile, n-hexane, and n-heptane in the presence of calcium. The current study showed that the accumulation of amino acid substitutions D43E, T118N, E226D, E250L, and N304E produced highly stable T1 mutant when hydrolyzing oil in selected organic solvents such as DMSO, n-hexane, and n-heptane. It is also believed that calcium ion plays important role in regulating lipase thermostability.

Dataset Information

Biological Degradation of Aflatoxin B₁ by Cell-Free Extracts of Bacillus velezensis DY3108 with Broad PH Stability and Excellent Thermostability.

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