Biodegradation of Aflatoxin B1 in the Baijiu Brewing Process by Bacillus cereus

Characterization and genomic analysis of Bacillus megaterium with the ability to degrade aflatoxin B1

Coix seed is a good product for both medicinal and food use, which is highly susceptible to aflatoxin B1 (AFB1) contamination during field transport, storage, and processing. The aim of this study is to find microbial strains that can solve the problem of contamination of coix seed. In this study, the AFB1-degrading microorganism SX1-1 was isolated and identified as a Bacillus megaterium based on morphology, microscopy, and 16S rDNA sequencing. The optimum culture conditions for SX1-1 to degrade AFB1 were determined to be 12 h. The optimum degradation conditions were 72 h, 57°C, and an initial pH of 8.0. The highest degradation of AFB1 was observed in the fermentation supernatant of the SX1-1 strain, with a degradation rate of 97.45%. In addition, whole-genome sequencing analysis of this strain revealed the presence of a number of enzymes that could potentially degrade AFB1. Importantly, SX1-1 was able to degrade AFB1-contaminated coix seed in situ by 50.06% after co-culture. In conclusion, this strain had a high AFB1 degradation ability, and has great potential and great application as a biocontrol agent for AFB1 degradation of coix seed.

Antimutagenic activity of different forms of Bifidobacterium lactis probiotic against aflatoxin B1 by Ames method

The health risks caused by aflatoxins, as one of the most important contaminants of human food and feed and the main cause of cancer, especially hepatocellular carcinoma (HCC) were investigated. The aim of the study was to assess the antimutagenic effects of Bifidobacterium lactis (B. lactis) probiotic against aflatoxin B1 (AFB1). The study was conducted with 27 treatments and three replications. The independent variables were aflatoxin concentrations at three levels of 5, 15, and 25 ng/g and probiotic content in three forms of cellular sedimentation (CS), cell-free supernatant (CFS), and cell suspension. The antimutagenic activity of B. lactis against AFB1 was measured. The lowest score of antimutagenic activity of B. lactis was observed in bacterial cellular sediment treatment at 107 CFU/g and 25 ng/g of AFB1 (20.8 ± 3.80%) and the highest score was achieved with cell suspension at 109 CFU/g and 5 ng/g of AFB1 (74.9 ± 7.11%). In addition, the lack of mutagenicity of probiotics was confirmed. Therefore, probiotics not only alleviate aflatoxin in food matrices and benefit the consumer, but also notably decrease mutagenicity of AFB1.

Isolation and Optimization of Aflatoxin B1 Degradation by Uniform Design and Complete Genome Sequencing of Novel Deep-Sea Kocuria rosea Strain 13

Aflatoxin B1 is a natural carcinogenic mycotoxin. The biological detoxification of aflatoxin could result in less environmental pollution, more moderate conditions, and less impact on food and feed, and be more convenient than physical and chemical methods. In this study, strain 13 with aflatoxin B1 degradation activity (67.47 ± 1.44%) was isolated and identified as Kocuria rosea. A uniform design was applied to optimize the degradation activity using a software Data Processing System, and a quadratic polynomial stepwise regression model was selected to investigate the relationships between the degradation rate and five independent variables. Furthermore, the optimal degradation conditions (culture temperature of 30 °C, culture time of 4.2 days, seawater ratio of 100%, pH of 7.11, and inoculation dosage of 0.09%) were verified with a degradation rate of 88 ± 0.03%, which was well matched with the predicted value (92.97%) of the model. Complete genome sequencing of Kocuria rosea, conducted with a combination of Illumina and single-molecule real-time sequencing, was used to analyze the genomic features and functions of the strain, which were predicted by the annotation based on seven databases, and may provide insights into the potential of Kocuria rosea, as well as providing a reference for degradation gene and protein mining. These results indicate that Kocuria rosea strain 13 has the ability to degrade aflatoxin B1 efficiently, and it also has the potential to provide aflatoxin-degrading enzymes.

Tuning Thermostability and Catalytic Efficiency of Aflatoxin-Degrading Enzyme by Error-prone PCR

In our previous work, a recombinant aflatoxin-degrading enzyme derived from Myxococcus fulvus (MADE) was reported. However, the low thermal stability of the enzyme had limitations for its use in industrial applications. In this study, we obtained an improved variant of recombinant MADE (rMADE) with enhanced thermostability and catalytic activity using error-prone PCR. Firstly, we constructed a mutant library containing over 5000 individual mutants. Three mutants with T₅₀ values higher than the wild-type rMADE by 16.5 °C (rMADE-1124), 6.5 °C (rMADE-1795), and 9.8 °C (rMADE-2848) were screened by a high-throughput screening method. Additionally, the catalytic activity of rMADE-1795 and rMADE-2848 was improved by 81.5% and 67.7%, respectively, compared to the wild-type. Moreover, structural analysis revealed that replacement of acidic amino acids with basic amino acids by a mutation (D114H) in rMADE-2848 increased the polar interactions with surrounding residues and resulted in a threefold increase in the t_1/2 value of the enzyme and made it more thermaltolerate. KEY POINTS: • Mutant libraries construction of a new aflatoxins degrading enzyme by error-prone PCR. • D114H/N295D mutant improved enzyme activity and thermostability. • The first reported enhanced thermostability of aflatoxins degrading enzyme better for its application.

Biocontrol Capabilities of Bacillus subtilis E11 against Aspergillus flavus In Vitro and for Dried Red Chili (Capsicum annuum L.)

As a condiment with extensive nutritional value, chili is easy to be contaminated by Aspergillus flavus (A. flavus) during field, transportation, and storage. This study aimed to solve the contamination of dried red chili caused by A. flavus by inhibiting the growth of A. flavus and detoxifying aflatoxin B₁ (AFB₁). In this study, Bacillus subtilis E11 (B. subtilis) screened from 63 candidate antagonistic bacteria exhibited the strongest antifungal ability, which could not only inhibit 64.27% of A. flavus but could also remove 81.34% of AFB₁ at 24 h. Notably, scanning electron microscopy (SEM) showed that B. subtilis E11 cells could resist a higher concentration of AFB₁, and the fermentation supernatant of B. subtilis E11 could deform the mycelia of A. flavus. After 10 days of coculture with B. subtilis E11 on dried red chili inoculated with A. flavus, the mycelia of A. flavus were almost completely inhibited, and the yield of AFB₁ was significantly reduced. Our study first concentrated on the use of B. subtilis as a biocontrol agent for dried red chili, which could not only enrich the resources of microbial strains for controlling A. flavus but also could provide theoretical guidance to prolong the shelf life of dried red chili.