Degradation of the herbicide bentazon as related to enzyme production by Phanerochaete chrysosporium in two solid substrate fermentation systems

Enzyme production and degradation of the herbicide bentazon by Phanerochaet e chrysosporium growing on straw (solid substrate fermentation, SSF) and th e effect of nitrogen and the hydraulic retention time (HRT) were studied us ing a small bioreactor and batch cultures. The best degradation of bentazon was obtained in the low nitrogen treatments, indicating participation of t he ligninolytic system of the fungus. The treatments that degraded bentazon also had manganese peroxidase (MnP) activity, which seemed to be necessary for degradation. Pure MnP (with Mn(II) and H2O2) did not oxidize bentazon. However, in the presence of MnP, Mn(II) and Tween 80, bentazon was slowly oxidized in a H2O2-independent reaction. Bentazon was a substrate of pure l ignin peroxidase (LiP) and was oxidized significantly faster (22,000-29,000 times) as compared to the MnP-Tween 80 system. Although LiP was a better e nzyme for bentazon oxidation in vitro, its role in the SSF systems remains unclear since it was detected only in treatments with high nitrogen and hig h HRT where no degradation of bentazon occurred. Inhibition of LiP activity may be due to phenols and extractives present in the straw.