Veterinary drug albendazole inhibits root colonization and symbiotic function of the arbuscular mycorrhizal fungus Rhizophagus irregularis

Abstract

Arbuscular mycorrhizal fungi (AMF) are plant symbionts that have a pivotal role in maintaining soil fertility and nutrient cycling. However, these microsymbionts may be exposed to organic pollutants like pesticides or veterinary drugs known to occur in agricultural soils. Anthelminthics are veterinary drugs that reach soils through the application of contaminated manures in agricultural settings. Their presence might threaten the function of AMF, considered as sensitive indicators of the toxicity of agrochemicals to the soil microbiota. We determined the impact of the anthelminthic compounds albendazole and ivermectin on the establishment and functionality of the symbiosis between the model-legume Lotus japonicus and the AMF Rhizophagus irregularis. Our analyses revealed negative effects of albendazole on the development and functionality of arbuscules, the symbiotic organelle of AMF, at a concentration of 0.75 μg g-1. The impairment of the symbiotic function was verified by the reduced expression of genes SbtM1, PT4 and AMT2;2 involved in arbuscules formation, P and N uptake, and the lower phosphorus shoot content detected in the albendazole-treated plants. Our results provide first evidence for the toxicity of albendazole on the colonization capacity and function of R. irregularis at concentrations that may occur in agricultural soils systematically amended with drug-containing manures.

Keywords: albendazole; arbuscular mycorrhizal fungi; plants; symbiosis; toxic effects; veterinary drugs.

Figure 1.

Arbuscular mycorrhizal fungi (AMF) root colonization levels after application of veterinary drugs. (A) Application of albendazole affects AMF root colonization. (B) Application of ivermectin does not affect AMF root colonization. Levels of AMF root colonization five weeks after the application of different concentrations of albendazole or ivermectin (or DMSO for the control treatment). Comparisons are between drug-treated and DMSO-treated (control) plants of L. japonicus. Statistical analysis was performed by t-tests: *P<0.05 (ns = not significant). No statistically significant difference was detected for invermectin treatments. (n = 5)

Figure 2.

Application of albendazole decreases phosphorus content in the plant shoot. Phosphorus content in the shoots of L. japonicus plants five weeks after the application of different concentrations of albenzole (or DMSO for the control treatment). Comparisons are between albendazole-treated and control plants. Statistical analysis was performed by t-tests: **P<0.01 (n = 4) (ns = not significant)

Figure 3.

Application of albendazole affects the expression levels of mycorrhizal marker genes. Ratios of gene expression levels in the roots of albendazole-treated to DMSO-treated (control) L. japonicus plants. Bars show means ± SE (n = 5). Comparisons are between albendazole-treated and control plants. Statistical analysis was performed by t-tests: ***P<0.001 (ns = not significant)

Figure 4.

Levels of albendazole in the plant growth substrate. Albendazole concentration was determined by HPLC analysis in sand samples from magentas boxes with or without plants and AMF. The initial concentration of albendazole in the solution was 5 mg L⁻¹. Statistical analysis was performed by one-way ANOVA followed by Tukey's post-hoc test (three technical replicates) (P<0,05). Significant differences are indicated by different letters.