Surface Binding of Aflatoxin B1 by Lactic Acid Bacteria

Specific lactic acid bacterial strains remove toxins from liquid media by physical binding. The stability of the aflatoxin B₁ complexes formed with 12 bacterial strains in both viable and nonviable (heat- or acid-treated) forms was assessed by repetitive aqueous extraction. By the fifth extraction, up to 71% of the total aflatoxin B₁ remained bound. Nonviable bacteria retained the highest amount of aflatoxin B₁. Lactobacillus rhamnosus strain GG (ATCC 53103) and L. rhamnosus strain LC-705 (DSM 7061) removed aflatoxin B₁ from solution most efficiently and were selected for further study. The accessibility of bound aflatoxin B₁ to an antibody in an indirect competitive inhibition enzyme-linked immunosorbent assay suggests that surface components of these bacteria are involved in binding. Further evidence is the recovery of around 90% of the bound aflatoxin from the bacteria by solvent extraction. Autoclaving and sonication did not release any detectable aflatoxin B₁. Variation in temperature (4 to 37°C) and pH (2 to 10) did not have any significant effect on the amount of aflatoxin B₁ released. Binding of aflatoxin B₁ appears to be predominantly extracellular for viable and heat-treated bacteria. Acid treatment may permit intracellular binding. In all cases, binding is of a reversible nature, but the stability of the complexes formed depends on strain, treatment, and environmental conditions.     

测定λ原噬菌体诱导频率的新方法

本文报道两种测定λ原噬菌体紫外诱导频率的新方法 - 菌落计数法和平板诱导法.将溶源菌液经紫外诱导暗培养稀释后直接涂布在平板上培养,根据平板上菌落形成单位数计算λ噬菌体紫外诱导频率.另一种是将溶源菌与指示菌混合制备的平板用紫外线诱导,根据平板上噬菌体形成单位确定λ噬菌体紫外诱导频率.这两种方法不仅能准确测定噬菌体紫外诱导频率,而且操作简便,节省时间和用具,重复性好.本研究还将冬虫夏草浸出汁与溶源菌混合后进行紫外辐射,通过几种方法进行比较,结果证明建立的新方法确实可行,易操作;同时也表明冬虫夏草具有较强的抗紫外辐射作用.     

Intestinal Mucus Alters the Ability of Probiotic Bacteria To Bind Aflatoxin B1 In Vitro

Several probiotics are known to bind aflatoxin B₁ (AFB₁) to their surfaces and to adhere to intestinal mucus. In this study, preincubation of two probiotic preparations with either AFB₁ or mucus reduced the subsequent surface binding of mucus and AFB₁, respectively, in a strain-dependent manner.     

Electron Microscopic Evidence for Linear Insertion of Bacteriophage MU-1 in Lysogenic Bacteria

Temperate bacteriophage Mu-1 was used to generate a lysogenic derivative of the F'lac episome of Escherichia coli. Intact, covalently circular molecules of F'lac and lysogenic F'lac Mu(+) deoxyribonucleic acid (DNA) were isolated and examined by electron microscopy. The mean contour lengths of F'lac and F'lac Mu(+) molecules were 37.6 +/- 0.4 mum and 53.2 +/- 0.4 mum, respectively. The mean difference, 15.6 mum, is similar to the mean contour length of 12.9 +/- 0.1 mum obtained for linear DNA molecules released by osmotic shock from mature phage Mu-1 virions. These results provide direct physical evidence that phage Mu-1 integrates by linear insertion of its genome into the DNA of lysogenic host bacteria. Chemical and physical analyses of phage Mu-1 DNA indicate that it is similar to E. coli DNA in respect of gross base composition, buoyant density, and melting temperature.     

Seasonal Abundance of Lysogenic Bacteria in a Subtropical Estuary

Seasonal changes in the abundance of inducible lysogenic bacteria in a eutrophic estuarine environment were investigated over a 13-month period. Biweekly water samples were collected from Tampa Bay, Fla., and examined for prophage induction by mitomycin C treatment. At the conclusion of the study, we determined that 52.2% of the samples displayed prophage induction, as indicated by significant increases in viral direct counts compared with uninduced controls. Samples that displayed prophage induction occurred during the warmer months (February through October), when surface water temperatures were above 19°C, and no induction was observed in November, December, or January. This study presents clear evidence that there is seasonal variation in the number of inducible lysogenic bacteria in an estuarine environment.     

Bioconversion of Aflatoxin G1 to Aflatoxin B3 by selected fungi

Aflatoxin G₁ (AFG₁) was transformed into aflatoxin B₃ (AFB₃) by the fungiRhodotorula sp,Sporobolomyces sp,Rhizopus oryzae NRRL395,Pythium ultimum, Aspergillus terreus, A clavatus and Penicillium frequentans grown in a medium containing AFG₁, Difco potato dextrose broth, yeast extract, and peptone both in liquid shaken cultures and in solid static cultures at 25°C in the dark. A maximum rate of transformation of 10 % was obtained after 2 to 3 weeks of incubation. The transformation was correlated with an increase in the pH of the media from 5.7 –5.9 to 8.3 – 8.8.Saccharomyces cerevisiae also transformed AFG₁ into AFB₃, but at a slower rate; the pH of the media did not reach above 8.0 until 5 weeks after incubation. No transformation was observed whenA niger andP chrysogenum were tested; in both cases, no increase in pH was noticed. However, some transformation of AFG₁ to AFB₃ by both fungi was observed when the initial pH of the media was adjusted to 9.0. The rate of transformation increased to 15 – 20% in the static culture where the same medium was adsorbed onto vermiculite andRhizopus andAspergilli gave the highest increase in AFB₃ yield.     

生物进化的"溶源菌"关系演变进程

从免疫学角度分析了病毒与噬菌体建立的“溶源菌”关系．提出了生物进化中的“溶源菌”进程观点,对一些生物进化问题做出了新的解释,包括生物在进化历程中如何抵抗疾病危害、保存物种并繁衍后代,寒武纪大爆发,生物进化在一定范围内出现的不连续性,生物间基因组的“C值悖理”及“重复基因序列”的由来等。结合转基因技术的成熟运用,提出了新的生物进化关系式:B=A x．有利于进化理论的深化完善。     

黄曲霉毒素B1生物脱毒的研究进展

黄曲霉毒素是一组由黄曲霉、寄生曲霉等多种真茵产生的次级代谢产物,具有强烈的毒性,可以引起动物肝脏肿大、病变甚至癌变,对人和家畜的健康产生极大的威胁。本文简介了黄曲霉毒素B_1的分子结构、理化性质、污染现状,综述了黄曲霉毒素B_1生物脱毒方面及其应用的研究进展,重点讲述通过微生物降解黄曲霉毒素B_1的研究近况。     

Accumulation of Incomplete Particles After UV-Light Induction of Haemophilus influenzae Lysogenic for Bacteriophage HP1c1

Temperate phage HP1c1 produces large quantities of incomplete phage-like particles when grown on Haemophilus influenzae BC200, a strain apparently cured of a common defective prophage.     

Improved Rapid Plate Method for the Isolation of Bacteriophages from Lysogenic Bacteria

A modification of a recently reported rapid plate method for the isolation of bacteriophages from lysogenic bacteria is described. The velveteen replica plate technique was used for inoculation of mitomycin C-induced colonies onto agar plates, and tetrazolium chloride was used to enhance detection of phage activity on replicated indicator plates.     

Induction of Phage Production in the Lysogenic Escherichia coli by Hydroxyurea

1) Hydroxyurea, a reversible DNA synthesis inhibitor, was used to study the mechanism of prophage λ induction in Escherichia coli K12. Induction of prophage was judged on two criteria: increase of phage-producing cells and loss of colony-forming ability of the cells. 2) Hydroxyurea induced an increase of phage-producing cells only in lysogenic strains known to be inducible with ultraviolet irradiation for prophage development and not in strains such as E. coli K12 (λind^–) or E. coli K12 recA (λ⁺). 3) When protein synthesis was inhibited, hydroxyurea did not increase phage-producing cells of lysogenic strains; it showed a bacteriocidal effect on lysogenic recA⁺ strains, but not on nonlysogenic strains. 4) The sensitivity of E. coli K12 recA to hydroxyurea was independent of whether or not the cells were lysogenic. 5) From the results it is suggested that certain steps leading to loss of colony-forming ability (i.e. prophage induction) do not require de novo protein synthesis but require the presence of the host recA⁺ gene.     

Aflatoxin B1 dihydrodiol antibody: production and specificity

A specific antibody for 2,3-dihydro-2,3-dihydroxyaflatoxin B1 (AFB1-diol) was prepared, and its reactivity was characterized for the major aflatoxin (AF) B1 (AFB1) metabolites. Reductive alkylation was used to conjugate AFB1-diol to ethylenediamine-modified bovine serum albumin (EDA-BSA) and horseradish peroxidase for use as an immunogen and an enzyme-linked immunosorbent assay (ELISA) marker, respectively. High reactant ratios, 1:5 and 1:10, for AFB1-diol-EDA-BSA (wt/wt) resulted in precipitated conjugates which were poorly immunogenic. However, a soluble conjugate obtained by using a 1:25 ratio of AFB1-diol to EDA-BSA could be used for obtaining high-titer AFB1-diol rabbit antibody within 10 weeks. Competitive ELISAs revealed that the AFB1-diol antibody detected as little as 1 pmol of AFB1-diol per assay. Cross-reactivity of AFB1-diol antibody in the competitive ELISA with AF analogs was as follows: AFB1-diol, 100%; AFB1, 200%; AFM1, 130%; AFB2a, 100%; AFG1, 6%; AFG2, 4%; aflatoxicol, 20%; AFQ1, 2%; AFB1-modified DNA, 32%; and 2,3-dihydro-2-(N7-guanyl)-3-hydroxy AFB1, 0.6%. These data indicated that the cyclopentanone and methoxy moieties of the AF molecule were the primary epitopes for the AFB1-diol antibody. The AFB1-diol competitive ELISA was subject to substantial interference by human, rat, and mouse serum albumins but not by BSA, Tris, human immunoglobulin G, or lysozyme. By using a noncompetitive, indirect ELISA with an AFB1-modified DNA solid phase, a modification level of one AFB1 residue for 200,000 nucleotides could be determined.     

Aflatoxin B1 alters protein phosphorylation in rat livers

A study was conducted on the effect of aflatoxin B1 on protein phosphorylation in rat livers by incubation of soluble and insoluble cell fractions with [gamma 32P] ATP. SDS-polyacrylamide gel electrophoresis indicated that a total of eight rat liver phosphoproteins were affected during a feeding period of 36 weeks on a carcinogenic aflatoxin B1-containing diet compared to the phosphoprotein patterns obtained from the livers of rats on a normal noncarcinogenic diet. The appearance of only two of these phosphoproteins were cAMP dependent. DEAE-cellulose chromatography employed to separate the different histone kinase activities in soluble rat liver cell fractions, showed that the specific activity of histone kinase I activity was increased but its total activity decreased while the histone kinase II activity stayed unchanged for rats submitted to the aflatoxin B1-containing diet compared to those on the normal noncarcinogenic diet.     

Aflatoxin B1 induced hepatocarcinogenesis in neonatal rats.

Role of cell replication on aflatoxin B1 (AFB1) induced hepatocarcinogenesis was investigated in neonatal rats showing persistence of cell replication in the liver for 21 days of post natal life. Adult (8-10 weeks old) rats displaying no hepatocytic proliferation served as controls. Three doses of AFB1 were administered to both the groups at intervals of 48 hr with the doses starting on 10th day of age in the neonatal group. Appearance of phenotypically altered preneoplastic hepatocytes was quantitated in both the groups. A significantly higher incidence of preneoplastic foci was recorded in neonatal rats as compared to adult animals. The results suggest that presence of cell replication in neonatal rats at the time of AFB1 administration enhances the process of hepatocarcinogenesis.     

Contamination of Red Chilli with Aflatoxin B1 in Pakistan

A survey of red chilli (Capsicum indicum) for contamination with aflatoxins was performed on different samples comprising whole, crushed and powdered red chilli collected from various stores located in the city of Karachi, Pakistan. Red chilli required rather rigorous clean-up procedure for removal of adulterants and interference resulting from various types of compounds. A modified Romer method followed by bi-directional thin layer chromatography (TLC) was used for the detection of aflatoxins and confirmatory tests were performed by spraying the TLC plates with 50% sulphuric acid and making the derivative with trifluoroacetic acid. Of all the 176 samples of red chilli examined, 66% were found to be contaminated with aflatoxin B₁. Generally, samples of red chilli exammined were found to be fairly low in aflatoxin B₁ content, whereas only seven samples were found to contain concentrations greater than 25 μg/kg of aflatoxin B₁.     

Stability of Aflatoxin B1 and Ochratoxin A in Brewing

The stability of aflatoxin B₁ and ochratoxin A in brewing was investigated by adding the purified toxins to the raw materials at 1 and 10 μg/g levels during mashing in a conventional micro-brewing process. The results indicate that both toxins are stable to heat and are insensitive to cooker mash treatment. Both mycotoxins were partially removed in the mashing and brewing processes. About 14 to 18% and 27 to 28% of the added toxins were found in the final beers brewed from starting materials containing 1 and 10 μg, respectively, of either toxin per g. The possible route of transmission of mycotoxins into beer is discussed.