Biodegradation of aflatoxin B1 by Bacillus subtilis YGT1 isolated from yoghurt

Abstract

Aflatoxin contamination of food products is recognised as a major food safety concern throughout the world because of its carcinogenic, mutagenic, and immunosuppressive effects on human health. Of the various types of aflatoxins, aflatoxin B1 (AFB1) is the ubiquitous and most threatening foodborne mycotoxin to humans. A wide range of detoxification methods is used to reduce the toxic effects of AFB1. In the present work, the ability of probiotics isolated from yoghurt (produced by bacterial fermentation of milk), “laban” (fermented milk beverage), and “idli” batter (fermented rice and black gram) in the detoxification of AFB1 was investigated under laboratory conditions. Among the four isolates from fermented foods evaluated, the isolate YGT1 from yoghurt showed the maximum (83.8%) degradation of AFB1 in Luria-Bertani (LB) liquid medium after 48 h of incubation at 30°C. The degradation of AFB1 by the probiotic isolate was further confirmed by liquid chromatography/mass spectrometry analysis. On the basis of 16S rRNA gene sequence analysis, the bacterial isolate YGT1 was identified as Bacillus subtilis. The culture supernatant and heat-treated culture supernatant (boiled for 30 min) of B. subtilis YGT1 also exhibited degradation of AFB1, thus suggesting the involvement of thermostable bioactive compound(s) in the degradation of AFB1. These results suggested that B. subtilis YGT1 isolated from yoghurt may be a promising candidate for exploitation in food and feed industries for the removal of AFB1.

Rice Weevil (Sitophilus oryzae L.) Gut Bacteria Inhibit Growth of Aspergillus flavus and Degrade Aflatoxin B1

“…Ali et al [60] reported that P. fluorescens strain SZ1 isolated from soil degraded 100% of AFG1 and 99% of aflatoxin B1, B2, and G2. Al-Mamari et al [19] found that live cells of B. subtilis YGT1 obtained from yogurt degraded 83.8% of AFB1 after 48 h of incubation at 30 • C. El-Nezami et al [71] showed that even heat-and acid-treated dead cells of L. rhamnosus GG could bind AFB1. The peptidoglycan in the cell wall of L. rhamnosus GG has been reported as crucial for binding AFB1 [72].…”

“…Xu et al [73] showed that B. shackletonii L7 significantly reduced AFB1 levels (92.1%), with the culture supernatant degrading more AFB1 than live cells or cell extracts. Al-Mamari et al [19] reported that the culture supernatant of B. subtilis YGT1 degraded 81.3% of AFB1 in culture medium after 48 h of incubation at 30 • C. The furofuran and lactone rings are the critical sites for the toxic effects of aflatoxins. Modifications to these ring structures typically lead to the loss of the toxic effects of aflatoxins [74,75].…”

“…After incubation, the culture (OD 600 of 1.0) was centrifuged at 14,000 rpm for 10 min, and cell-free supernatant was collected. To 1 mL of the supernatant, 1 µL of AFB1 (1000 ppb) was added and incubated at 30 °C for 48 h. Subsequently, the AFB1 in the mixture was extracted using chloroform (1:1, v / v ), and its content was determined by LC-MS, and the degraded products of AFB1 were analyzed as described by Al-Mamari et al [ 19 ]. A control sample was prepared using uninoculated NB (1 mL) containing AFB1 (1000 ppb) and processed in the same manner.…”

“…Subsequently, an equal volume of chloroform was added to the supernatant, mixed well, and briefly centrifuged. The chloroform fraction was collected in a new tube and dried in a water bath at 60 • C. The residue in the tube was dissolved in methanol, and AFB1 content in the sample was determined by liquid chromatography-mass spectrometry (LC-MS) as per the analysis conditions specified by Al-Mamari et al [19]. A control sample was prepared using uninoculated NB (1 mL) containing AFB1 (1000 ppb) and processed in the same manner.…”

“…and detoxifying aflatoxin-contaminated agricultural products [ 17 ]. Several strains of lactic acid bacteria and yeast can bind to mycotoxins and reduce their bioavailability in foods or feeds [ 14 , 18 , 19 ]. In addition, the microbial enzymes can transform mycotoxins, further reducing their toxicity before excretion [ 20 ].…”