The Importance of pH on the Biotransformation of Bromoxynil by Microbacterium imperiale CBS 498-74 Resting Cells

This work enlarges our previous results (Pasquarelli et al., 2015) on the effect of pH on the bioconversion of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) using Microbacterium imperiale CBS 498-74 resting cells. Their sequential enzymes, nitrile hydratase and amidase, which operate in cascade, transform the nitrile into the corresponding acid, via an amide as intermediate. This paper highlights the influence of different pH on the kinetic parameters, Vmax and KM, the stability of the enzymes and the completeness of bromoxynil bioconversion in batch reactors. Results from continuous stirred UF-membrane reactors (CSMR) suggest, for real application and high conversion yield (near 75% for more than 180 h continuous process), to operate at pH 6.5 realising the best compromise between enzyme stability, high Vmax. This even if at pH 7.0 the enzyme half life is higher.