Novel Aflatoxin-Degrading Enzyme from Bacillus shackletonii L7

Abstract

Food and feed contamination by aflatoxin (AF)B1 has adverse economic and health consequences. AFB1 degradation by microorganisms or microbial enzymes provides a promising preventive measure. To this end, the present study tested 43 bacterial isolates collected from maize, rice, and soil samples for AFB1-reducing activity. The higher activity was detected in isolate L7, which was identified as Bacillus shackletonii. L7 reduced AFB1, AFB2, and AFM1 levels by 92.1%, 84.1%, and 90.4%, respectively, after 72 h at 37 °C. The L7 culture supernatant degraded more AFB1 than viable cells and cell extracts; and the degradation activity was reduced from 77.9% to 15.3% in the presence of proteinase K and sodium dodecyl sulphate. A thermostable enzyme purified from the boiled supernatant was designated as Bacillus aflatoxin-degrading enzyme (BADE). An overall 9.55-fold purification of BADE with a recovery of 39.92% and an activity of 3.85 × 103 U·mg−1 was obtained using chromatography on DEAE-Sepharose. BADE had an estimated molecular mass of 22 kDa and exhibited the highest activity at 70 °C and pH 8.0, which was enhanced by Cu2+ and inhibited by Zn2+, Mn2+, Mg2+, and Li+. BADE is the major protein involved in AFB1 detoxification. This is the first report of a BADE isolated from B. shackletonii, which has potential applications in the detoxification of aflatoxins during food and feed processing.

Identification of the Anti-Aflatoxinogenic Activity of Micromeria graeca and Elucidation of Its Molecular Mechanism in Aspergillus flavus

“…Recent studies have pointed out the use of physio-chemical approaches to counteract aflatoxin contamination [8,9] while others were based on the detoxification properties or the protective physiological effect of bacterial metabolites or natural extracts used as feed supplements [10,11,12,13]. Although proven to be efficient, these approaches remain strictly restricted to animal feed.…”

The Toxic Effects of Aflatoxin B1: An Update

“…The efficacy of these approaches has been high, but more information based on further practice on real food substrates is necessary. As is the case with all the biological control methods, the time of treatment is still long, taking several days to complete which may not be feasible in large-scale applications [119][120][121]. Another disadvantage lies in an uncertainty of the end products of the treatments, which makes the safety of treated foods hard to determine.…”

Retrospective and Prospective Look at Aflatoxin Research and Development from a Practical Standpoint

“…Pseudomonas spp. Stenotrophomonas spp., Arthrobacter spp., and members of the family Flavobacteriaceae were shown in vitro to produce aflatoxin-degrading enzymes causing a significant reduction (>90%) in the levels of AFB1, AFM1 and/or AFB2 [217][218][219][220]. However, for these microorganisms to be effective in vivo, they have to colonize the intestinal tract and express sufficient levels of the aflatoxin-degrading enzymes.…”

“…This may require specific physicochemical conditions and the presence of inducing factors for the enzyme to be optimally produced and active. A highly active aflatoxin-degrading enzyme produced by Bacillus shackletonii was indeed shown to require specific inducers for their expression and to be degraded by proteinase K which, in addition to the aerobic character of the producing bacterium, limit drastically its potential use as a probiotic strain in a chemoprotective strategy [218]. A suitable microorganism for a chemoprotection strategy should be able to adapt to the prevailing ecological conditions of the GI tract (pH, temperature, red/ox potential, and oxygen), to withstand the presence of inhibitory substances, e.g., bile and bile salts, and to compete with co-existing microorganisms, among other general requirements for a microbial strain to have the probiotic status [221].…”