Evaluation of Phenolic Compound Toxicity Using a Bioluminescent Assay with the Fungus Gerronema viridilucens.

Basidiomycetes (phylum Basidiomycota) are filamentous fungi characterized by the exogenous formation of spores on a club-shaped cell called a basidium that are often formed on complex fruiting bodies (mushrooms). Many basidiomycetes serve an important role in recycling lignocellulosic material to higher trophic levels, and some show symbiotic relationships with plants. All known bioluminescent fungi are mushroom-forming basidiomycetes in the order Agaricales. Hence, the disruption of the basidiomycete community can entirely compromise the carbon cycle in nature from fungi to higher trophic levels. The fungus Gerronema viridilucens was used in the present study to investigate the toxicity of a phenolic compound series based on the inhibition of its bioluminescence. The median effect concentration (EC50) obtained from curves of bioluminescence inhibition versus log [phenolic compound] showed that 2,4,6-trichlorophenol was the most toxic compound in the series. The log EC50 values of all phenolic compounds were then used for the prediction of their toxicity. The univariate correlation of log EC50 values obtained from 6 different phenolic compounds was stronger with the dissociation constant (pKa ) than with 1-octanol/water partition coefficient (KOW ). Nevertheless, the toxicity can be better predicted by using both parameters, suggesting that the phenol-driven uncoupling of fungus mitochondrial adenosine triphosphate synthesis is the origin of phenolic compound toxicity to the test fungus. Environ Toxicol Chem 2020;39:1558-1565. © 2020 SETAC.

Early postnatal, but not late, exposure to chemical ambient pollutant 1,2-naphthoquinone increases susceptibility to pulmonary allergic inflammation at adulthood.

High diesel exhaust particle levels are associated with increased health effects; however, knowledge on the impact of its chemical contaminant 1,2-naphthoquinone (1,2-NQ) is limited. We investigated whether postnatal and adult exposures to 1,2-NQ influence allergic reaction and the roles of innate and adaptive immunity. Male neonate (6 days) and adult (56 days) C57Bl/6 mice were exposed to 1,2-NQ (100 nM; 15 min) for 3 days, and on day 59, they were sensitized and later challenged with ovalbumin (OVA). Airway hyper-responsiveness (AHR) and production of cytokines, immunoglobulin E (IgE) and leukotriene B4 (LTB4) were measured in the airways. Postnatal exposure to 1,2-NQ activated dendritic cells in splenocytes by increasing expressing cell surface molecules (e.g., CD11c). Co-exposure to OVA effectively polarized T helper (Th) type 2 (Th2) by secreting Th2-mediated cytokines. Re-stimulation with unspecific stimuli (PMA and ionomycin) generated a mixed Th1 (CD4(+)/IFN-γ(+)) and Th17 (CD4(+)/IL-17(+)) phenotype in comparison with the vehicle-matched group. Postnatal exposure to 1,2-NQ did not induce eosinophilia in the airways at adulthood, although it evoked neutrophilia and exacerbated OVA-induced eosinophilia, Th2 cytokines, IgE and LTB4 production without affecting AHR and mast cell degranulation. At adulthood, 1,2-NQ exposure evoked neutrophilia and increased Th1/Th2 cytokine levels, but failed to affect OVA-induced eosinophilia. In conclusion, postnatal exposure to 1,2-NQ increases the susceptibility to antigen-induced asthma. The mechanism appears to be dependent on increased expression of co-stimulatory molecules, which leads to cell presentation amplification, Th2 polarization and enhanced LTB4, humoral response and Th1/Th2 cytokines. These findings may be useful for future investigations on treatments focused on pulmonary illnesses observed in children living in heavy polluted areas.

Current status of research on fungal bioluminescence: biochemistry and prospects for ecotoxicological application.

Over the last half decade the study of fungal bioluminescence has regained momentum since the involvement of enzymes has been confirmed after over 40 years of controversy. Since then our laboratory has worked mainly on further characterizing the substances involved in fungal bioluminescence and its mechanism, as well as the development of an ecotoxicological bioluminescent assay with fungi. Previously, we proved the involvement of a NAD(P)H-dependent reductase and a membrane-bound luciferase in a two-step reaction triggered by addition of NAD(P)H and molecular oxygen to generate green light. The fungal luminescent system is also likely shared across all lineages of bioluminescent fungi based on cross-reaction studies. Moreover, fungal bioluminescence is inhibited by the mycelium exposure to toxicants. The change in light emission under optimal and controlled conditions has been used as endpoint in the development of toxicological bioassays. These bioassays are useful to better understand the interactions and effects of hazardous compounds to terrestrial species and to assist the assessment of soil contaminations by biotic or abiotic sources. In this work, we present an overview of the current state of the study of fungal luminescence and the application of bioluminescent fungi as versatile tool in ecotoxicology.