Sensitivity of laccase activity to the fungicide tebuconazole in decomposing litter.

The present study investigates the sensitivity of laccase activity to the fungicide tebuconazole (TBZ) in order to seek for new functional toxicity descriptors in aquatic microbial communities associated to decomposing litter. With this aim, we analyzed the sensitivity of laccase from the different microbial components (fungi and bacteria growing separately and in co-existence), as well as that of their corresponding enzyme fractions (cell bound and diffusible), forming microbial communities in Alnus glutinosa leaves. Results show that fungi are pivotal for laccase activity in leaves and that their activity is repressed when they co-exist with bacteria. The sensitivity of laccase activity to the TBZ was only detectable in leaves colonized by fungi separately (Alatospora acuminata populations), but absent in those colonized by bacteria separately and/or mixed fungi plus bacteria. Specifically, the increase of TBZ concentration enhances laccase activity in Alatospora acuminata populations but decreases ergosterol concentration as well as the amount of 18S RNA gene copies. This activity response suggests a detoxification mechanism employed by the fungus in order to reduce TBZ toxicity. Besides, enzyme fractioning showed that laccase activity in the cell bound fraction (76% of the total activity) was sensitive to the fungicide, but not that in the diffusible fraction (24% of total activity). Hence, TBZ would influence laccase activity in the presence of fungal cells but not in enzymes already synthesized in the extracellular space. The present study highlights the importance of the biological complexity level (i. e. population, community, ecosystem) when seeking for appropriate functional ecotoxicity descriptors in aquatic microbial communities.