Laccases are valuable enzymes as an excellent ecological alternative for bioremediation issues because they can oxidize persistent xenobiotic compounds. The production and characterization of extracellular laccases from saprotrophic fungi from disturbed environments have been scarcely explored, even though this could diversify their functional characteristics and expand the conditions in which they carry out their catalysis. Agrocybe pediades, isolated from a disturbed forest, produces an extracellular laccase in liquid culture. The enzyme was purified, identified and characterized. Copper and hexachlorobenzene do not function as inducers for the laccase produced. Partial amino acid sequences were obtained by LC-MS/MS that share similarity with laccases from other fungi. Purified laccase is a monomer with a molecular mass between 55–60 kDa and had an optimum activity at pH 5.0 and the optimum temperature at 45 °C using 2,6-dimethoxyphenol (2,6-DMP) as substrate. The K_m and V_max also determined with 2,6-DMP were 100 μM and 285 μmol∙min⁻¹∙mg⁻¹, respectively, showing that the laccase of A. pediades has a higher affinity for this substrate than that of other Agaricales. These features could provide a potential catalyst for different toxic substrates and in the future laccase could be used in environmental recovery processes.

The aim of this study was to assess the levels of some persistent organic pollutants in the surface sediments from the Zahuapan and Atoyac rivers (Tlaxcala, Mexico), as well as to determine the genotoxic potential, by the micronucleus test in Vicia faba, of the sediments and agricultural soils irrigated with water from these rivers. This document is the first study on the presence of POPs in surface sediments of the above-mentioned rivers; among the compounds analyzed are the HCH isomers, DDT and its metabolite DDE, HCB, mirex, aldrin, and 41 PCB congeners. The concentrations of HCB, ΣDDTs, ΣHCHs, and ΣPCBs ranged from 138–510, 45–450, 3–27, and 59–1876 μg kg⁻¹ dry weight, respectively. The highest levels of HCB, HCH isomers, and PCB congeners were found in the Atoyac River, and these compounds have the potential for causing an environmental impact. On the other hand, biological testing shows that both sediments and agricultural soils possess a genotoxic potential, given that the micronuclei frequency in V. faba is increased.

LEAD EXPOSURE: POTTERY IMPACT IN TLAXCALA, MEXICO

Cantharellus cibarius is one of the most important wild, edible, and ectomycorrhizal mushrooms growing at La Malinche National Park, Tlaxcala, Mexico; therefore, the assessment of its biological properties is of great interest to know its potential as an alternative treatment to chemopreventive strategies when it is consumed as part of a diet. Comet assay was used to evaluate the antigenotoxic properties of several concentrations of aqueous extracts (0.0125, 0.025, 0.05, 0.1, and 0.2% w/v) prepared at room temperature (22 ± 2°C). As a test system we used human mononuclear cells exposed to methyl methanesulphonate (MMS) in vitro according to 3 different protocols: previous, simultaneous, and posterior. Previous (0.0125%) and simultaneous (0.1%) treatments resulted in the highest inhibitory efficiency. In the former, the cells assessed showed a tail length of 94.9 ± 64 µm; in the latter, the tails measured 106.2 ± 40 µm. Resulting percentages of reduction in damage were 236% and 196.1%, respectively. We did not obtain a dose-dependent response. The mean tail length for each protocol (previous, 133.1 ± 80 µm; simultaneous, 127.8 ± 57 µm; posterior, 146.3 ± 74 µm) was statistically significant with regard to the positive control (MMS).

A wide variety of biological functions, including those involved in the morphogenesis process of basidiomycete fungi, have been attributed to laccase enzymes. In this work, RNA interference (RNAi) was used to evaluate the role of the laccase (lacc2) gene of Pleurotus ostreatus PoB. Previously, transformant strains of P. ostreatus were obtained and according to their level of silencing they were classified as light (T7), medium (T21) or severe (T26 and T27). The attenuation of the lacc2 gene in these transformants was determined by RT-PCR. Silencing of lacc2 resulted in a decrease in laccase activity between 30 and 55%, which depended on the level of laccase expression achieved. The silenced strains (T21, T26, and T27) displayed a delay in the development of mycelium on potato dextrose agar (PDA) medium, whereas in the cultures grown on wheat straw, we found that these strains were incapable of producing aerial mycelium, primordia, and fruiting bodies. Scanning electron microscopy (SEM) showed the presence of toxocyst-like structures. The highest abundance of these structures was observed in the wild-type (PoB) and T7 strains. However, the abundance of toxocysts decreased in the T21 and T26 strains, and in T27 they were not detected. These results suggest that the presence and abundance of toxocyst-like structures are directly related to the development of fruiting bodies. Furthermore, our data confirm that lacc2 is involved in the morphogenesis process of P. ostreatus.