Degradation of diclofenac by B. subtilis through a cytochrome P450-dependent pathway

Abstract Diclofenac exerts the highest level of acute toxicity among tested non-steroidal anti-inflammatory drugs. Although there are many reports on the microbial degradation of diclofenac, gaps remain in the knowledge related to the degradation process, especially that by Bacillus subtilis. In this study, we used B. subtilis 168trpc2 and its cytochrome P450 genetic defect strains B. subtilis Δ yrhJ and B. subtilis Δ yjiB to identify the key limiting protein and factor in diclofenac degradation. The results showed that in 72 h, B. subtilis 168trpc2 degraded 88.3% of diclofenac, whereas B. subtilis Δ yrhJ and B. subtilis Δ yjiB degraded 10% and 21%, respectively. These results illustrate that cytochrome P450 is essential for diclofenac degradation. The hydroxylation product of B. subtilis 168trpc2 is 5-OH-diclofenac, whereas the genetic defect strains generate the hydroxylation products 5-OH-diclofenac and 4ʹ-OH-diclofenac. Hydroxydiclofenac can subsequently be dechlorinated; through CO2 loss and C-N bond cleavage wherein dechlorination is the central step. This study provides direct evidence that cytochrome P450 determines the position of diclofenac hydroxylation and that hydroxydiclofenac can be subsequently degraded.