Antiparasitic potential of agrochemical fungicides on a non-target aquatic model (Daphnia × Metschnikowia host-parasite system)

Ecological impacts of agrochemical and pharmaceutical antifungals on a non-target aquatic host-parasite model

Agrochemical fungicides and their pharmaceutical counterparts are a major anthropogenic threat to the biodiversity of freshwater ecosystems as they affect non-target organisms (including aquatic fungi) and disrupt the processes in which they intervene. The goal of this work was to assess the effects of four common agricultural fungicides differing in their modes of action (azoxystrobin, carbendazim, folpet, and mancozeb) and an antifungal pharmaceutical (clotrimazole) on a host × parasite experimental model. We conducted 21-day life history experiments with Daphnia magna (the host) in the absence or presence of Metschnikowia bicuspidata (a microparasitic yeast) to evaluate the effect of each fungicide on the outcome of this relationship (disease) and the fitness of both host and parasite. Interactive but context-dependent effects were observed in D. magna life history responses upon concomitant exposure to parasite and toxicant. The parasite had a drastic negative effect on host survival and reproduction. Carbendazim, clotrimazole and folpet significantly decreased host fitness. In some cases (depending on the combination of toxicant and measured endpoint), simultaneous exposure of the host to the parasite and fungicides led to a slight decrease in host reproduction, which was absent when only the fungicide was present. In two other cases, the fungicide interfered with the host-parasite relationship: azoxystrobin had an impact on infection intensity (decreasing spore load per host), whereas clotrimazole demonstrated a strong antiparasitic effect, clearing all signs of infection (0 % prevalence). These findings emphasize the context-dependent nature of the interaction between pollution and disease.

Discovery of New Antifungal Polyketides Cladrioides A-N against Phytopathogenic Fungi from Cladosporium cladosporioides LD-8

During the search for natural fungicides, 14 new australifungin analogues cladrioides A-S (1-14) and two known ones (15 and 16) were obtained from Cladosporium cladosporioides LD-8. Their structures were elucidated by comprehensive analysis of NMR and HRESIMS data, as well as ECD calculations. Compounds 1 and 2 possess a novel 6/6/5-fused tricyclic scaffold. Most of the compounds exhibited remarkable antifungal activities against the tested phytopathogenic fungi. Among them, compounds 7, 10, and 16 showed excellent activities with IC50 values ranging from 1.71 to 16.63 μg/mL. Their inhibitory activities against A. brassicicola and A. alternata were higher than that of the commercial fungicide hymexazol. Compound 16 displayed potent in vivo antifungal activity against A. solani at 100 μg/mL with an inhibitory rate of 96.82%. The structure-activity relationship of antifungal australifungin analogues was analyzed for the first time. Therefore, our study provides promising candidates for the development of new fungicides for plant protection.

Direct and indirect effects of chemical pollution: Fungicides alter growth, feeding, and pigmentation of the freshwater detritivore Asellus aquaticus

Anthropogenic chemical pollutants, such as fungicides, pose significant threats to natural ecosystems. Although the direct impacts of numerous chemicals are well-documented in simple environmental contexts, their indirect impacts are poorly understood. This study used two individual level laboratory experiments to assess direct and indirect effects of fungicides on the isopod Asellus aquaticus, a keystone detritivore in freshwater systems. First, a range-finding assay on three widely used fungicides (Fluazinam, Tebuconazole, Urea) showed that Tebuconazole had the strongest concentration-dependent negative effects on A. aquaticus growth and food consumption. Second, a factorial experiment using Tebuconazole assessed its direct and diet-mediated effects and showed that Tebuconazole reduced growth, feeding, and pigmentation through both pathways. The results indicate that assessing only direct impacts of toxic chemicals could overlook critical interactions that are relevant in natural systems, such as those associated with diet. Our study highlights the importance of considering both direct and indirect effects in environmental toxicology to better understand the full impacts of chemical pollutants in nature.

Current trends and mismatches on fungicide use and assessment of the ecological effects in freshwater ecosystems

Despite increasing evidence of off-site ecological impacts of pesticides and policy efforts worldwide, pesticide use is still far from being ecologically sustainable. Fungicides are among the most sold classes of pesticides and are crucial to ensure global food supply and security. This study aimed to identify potential gaps of knowledge and mismatches between research and usage data of fungicides by: (i) systematizing the current trends in global sales of fungicides, focusing on the European context in particular (where they are proportionally important); (ii) reviewing the scientific literature on the impacts of synthetic fungicides on non-target freshwater organisms. Sales data revealed important global and regional asymmetries in the relative importance of fungicides and the preferred active ingredients. The literature review on the ecological effects of fungicides disclosed a mismatch between the most studied and the most sold substances, as well as a bias towards the use of single species assays with standard test organisms. To ensure a proper evaluation, risk scenarios should focus on a regional scale, and research agendas must highlight sensitive aquatic ecorreceptors and improve the crosstalk between analytical and sales data.

Strobilurin fungicide increases the susceptibility of amphibian larvae to trematode infections

The global rise in fungal pathogens has driven the increased usage of fungicides, yet our understanding of their ecotoxicity remains largely limited to acute toxicity. While such data is critical for projecting the risk of fungicide exposure to individual species, the contamination of natural systems with fungicides also has the potential to alter species interactions within communities including host-parasite relationships. We examined the effects of the fungicide pyraclostrobin on the susceptibility of larval American bullfrogs (Rana catesbeiana) to trematode (echinostome) infections using a controlled laboratory experiment. Following a 2-wk exposure to 0, 1.0, 5.2, or 8.4 µg/L of pyraclostrobin, tadpoles were then exposed to parasites either in the 1) presence (continued/simultaneous exposure) or 2) absence (fungicide-free water) of pyraclostrobin. We found that when exposed to pyraclostrobin during parasite exposure, meta cercariae counts increased 4 to 8 times compared to control tadpoles. Additionally, parasite loads were approximately 2 times higher in tadpoles with continued fungicide exposures compared to tadpoles that were moved to fresh water following fungicide exposure. This research demonstrates that fungicides at environmentally relevant concentrations can indirectly alter host-parasite interactions, which could elevate disease risk. It also underscores the need for studies that expand beyond traditional toxicity experiments to assess the potential community and ecosystem-level implications of environmental contaminants.

Implications of biotic factors for toxicity testing in laboratory studies

There is an emerging call from scientists globally to advance the environmental relevance of laboratory studies, particularly within the field of ecotoxicology. To answer this call, we must carefully examine and elucidate the shortcomings of standardized toxicity testing methods that are used in the derivation of toxicity values and regulatory criteria. As a consequence of rapidly accelerating climate change, the inclusion of abiotic co-stressors are increasingly being incorporated into toxicity studies, with the goal of improving the representativeness of laboratory-derived toxicity values used in ecological risk assessments. However, much less attention has been paid to the influence of biotic factors that may just as meaningfully impact our capacity to evaluate and predict risks within impacted ecosystems. Therefore, the overarching goal is to highlight key biotic factors that should be taken into consideration during the experimental design and model selection phase. SYNOPSIS: Scientists are increasingly finding that lab reared results in toxicology might not be reflective of the external wild environment, we highlight in this review some key considerations when working between the lab and field.

Interaction effect of fungicide and chitosan on non-target lichenized fungi

Excessive use of plant growth stimulants and pesticides is currently a considerable problem, especially in agriculture, horticulture, and arboriculture. Understanding the impacts of these compounds and their combinations on non-target organisms is crucial to minimize unintended consequences, while maintaining their use in plant protection. The aim of this study was to test how long-term spraying with different solutions of natural biostimulator chitosan, synthetic fungicide Switch 62.5 WG, and their combinations affects the physiology of epiphytic lichen Xanthoria parietina naturally occurring in fruit orchards and farmlands. We showed that fungicides composed of fludioxionil and cypronidil, as well as the combined use of such fungicides together with chitosan, can cause the considerable impairment of lichen physiology, and these disturbances relate to both algal and fungal partners of the symbiotic association. This negative effect was especially visible in the loss of cell membrane integrity, the high level of membrane lipid peroxidation, and changes in chlorophyll fluorescence parameters on the last day of the experiment. The combined use of these agents also leads to clear disturbances in the functioning of the mitochondrial respiratory chain, which was manifested by increased NADH dehydrogenase activity, while the use of these compounds separately led to a decrease in the activity of this enzyme. We concluded that the regular use of these agents in fruit tree cultivation may cause serious ecological consequences for epiphytic lichen communities as a result of the death of lichen thalli. This study suggests that the impact of some plant protection agents, both individually and in combinations, merits further attention in terms of their impact on non-target fungi.

Moving beyond standard toxicological metrics: The effect of diclofenac on planktonic host-parasite interactions

Pharmaceuticals are increasingly released into surface waters and therefore ubiquitous in aquatic systems. While pharmaceuticals are known to influence species interactions, their effect on host-parasite interactions is still underexplored despite potential ecosystem-level consequences. Here, we ask whether diclofenac, a widely used non-steroid anti-inflammatory drug, affects the interaction between a phytoplankton host (Staurastrum sp.; green alga) and its obligate fungal parasite (Staurastromyces oculus; chytrid fungus). We hypothesized that the effect of increasing diclofenac concentration on the host-parasite system depends on parasite exposure. We assessed acute and chronic effects of a wide range of diclofenac concentrations (0-150 mg/L) on host and parasite performance using a replicated long gradient design in batch cultures. Overall system response summarizing parameters related to all biotic components in an experimental unit i.e., number of bacteria and phytoplankton host cells along with photosynthetic yield (a measure of algal cell fitness), depended on diclofenac concentration and presence/absence of parasite. While host standing biomass decreased at diclofenac concentrations >10 mg/L in non-parasite-exposed treatments, it increased at ≥10 mg/L in parasite-exposed treatments since losses due to infection declined. During acute phase (0-48 h), diclofenac concentrations <0.1 mg/L had no effect on host net-production neither in parasite-exposed nor non-parasite-exposed treatments, but parasite infection ceased at 10 mg/L. During chronic phase (0-216 h), host net-production declined only at concentrations >10 mg/L in non-parasite-exposed cultures, while it was overall close to zero in parasite-exposed cultures. Our results suggest that chytrid parasites are more sensitive to diclofenac than their host, allowing a window of opportunity for growth of phytoplankton hosts, despite exposure to a parasite. Our work provides a first understanding about effects of a pharmaceutical on a host-parasite interaction beyond those defined by standard toxicological metrics.