Aflatoxin B1 Degradation by Flavobacterium aurantiacum in the Presence of Reducing Conditions and Seryl and Sulfhydryl Group Inhibitors

Abstract

This study was undertaken to determine the effects of reducing conditions (l-cysteine) and seryl (phenylmethylsulfonyl fluoride) and sulfhydryl (divalent cadmium) group inhibitors on aflatoxin B1 (AFB1) degradation by Flavobacterium aurantiacum. High-performance liquid chromatography was used to determine AFB1 concentrations in 72-h cultures of F. aurantiacum. The addition of 0.1, 1, or 10mM l-cysteine did not have any significant effect on AFB1 degradation by these cultures after incubation for 4, 24, or 48 h (P > 0.05). The addition of 0.1mM phenylmethylsulfonyl fluoride did not significantly decrease AFB1 degradation (P > 0.05), but 1mM phenylmethylsulfonyl fluoride significantly decreased AFB1 degradation after 4, 24, and 48 h of incubation (P ≤ 0.05). No significant difference in AFB1 degradation was obtained with 0.1mM Cd2+ after 4, 24, or 48 h of incubation (P > 0.05). The addition of 1 and 10mM Cd2+ significantly decreased AFB1 degradation compared with the cells containing AFB1 alone after 4 and 24 h (P ≤ 0.05). The addition of chelators, 1mM EDTA and 1mM o-phenanthroline, did not result in removal of inhibition of AFB1 degradation observed with 1 and 10mM Cd2+. Higher concentration of chelators (>1 mM) are necessary to overcome the inhibitory effect. Further work on the cellular fractions and/or crude enzyme preparations is necessary to determine if indeed sulfhydryl and seryl groups of the enzymes are involved in AFB1 degradation (by maintaining either the structure or function of the enzyme).