Extracellular laccase activity and transcript levels of putative laccase genes during removal of  the xenoestrogen technical nonylphenol by the aquatic hyphomyceteClavariopsis aquatica

Abstract

We investigated the influence of potential laccase inducers with environmental relevance on extracellular laccase activity and removal of the xenoestrogen technical nonylphenol (tNP) by the aquatic hyphomycete Clavariopsis aquatica. Concomitantly, we identified two putative laccase gene fragments (Icc1 and Icc2) and have followed their expression during removal of tNP under different conditions. Our results indicate a significant effect of copper on extracellular laccase activity in supernatants of fungal cultures. Laccase activity was highest in the presence of copper when added together with vanillic acid, followed by copper when used alone. Only slight laccase activities were recorded in the presence of only vanillic acid, whereas in the absence of either compound laccase activities were negligible. Laccase activity was well correlated with the removal efficiency of tNP, indicating the involvement of laccase in tNP bioconversion. Overall, Icc2 was less expressed than Icc1. The expression of Icc1 and Icc2 correlated only partially with the measured laccase activity, suggesting the existence of cell-associated laccase fractions not detectable in fungal culture supernatants and/or the existence of additional laccase genes.