Enhanced production of benzoylformate reductase in Enterococcus faecalis under oxidative stress established by natural electron carriers

Enhancement of the production of benzoylformate reductase (BFR) was attempted under oxidative stress established by natural electron carriers. α-lipoic acid (LA), flavin adenine dinucleotide (FAD), and ubiquinone (UQ) did not inhibit growth of E. faecalis when their concentrations were as high as 10 μM, while H₂O₂ and methyl viologen (MV²⁺) inhibited the bacterial growth. BFR activity in the bacterial extract had increased rapidly after 1 h of cultivation after the addition of 4 μM of natural electron carriers, and the activity was maintained during further cultivation. BFR activity of the cells treated with the natural electron carriers was 40% higher than that of the control. In the presence of 4 μM H₂O₂ and MV²⁺, BFR activity increased, reaching the highest activity at about 5 h cultivation, and then decreased with further cultivation. It seems that natural electron carriers not only stimulate the induction of BFR, but also stabilize the enzyme. BFR was hardly affected by LA, FAD, and UQ, while H₂O₂ and MV²⁺ inactivated the crude enzyme. The decrease of BFR activity in the presence of H₂O₂ and MV²⁺ might be ascribed to inactivation of the enzyme by the oxidants.