Molecular toxicity of earthworms induced by cadmium contaminated soil and biomarkers screening

Earthworms (Eisenia fetida) were used to study the impact of low-dose cadmium in treated artificial soil (0, 0.6, 3, 6, 15, 30 mg/kg) and contaminated natural soil (1.46 mg/kg). The changes of earthworms' physiological related gene expressions of metallothionein (MT), annetocin, calreticulin and antimicrobial peptides were detected using real-time PCR after a 70-day incubation period. The results showed that low doses of cadmium could up regulate earthworms' MT and down regulate annetocin gene expression and show a significant positive and negative correlation respectively. The expression of two other genes, calreticulin and anti-microbial peptides, was induced at low doses of cadmium (highest gene expression at 0.6 mg/kg for calreticulin and 6 mg/kg for anti-microbial peptides) and inhibited at high doses. No significant correlation was found for these two genes. This study shows that MT and annetocin genes expression found in earthworms in contaminated soil have the potential to be developed as biomarkers of soil cadmium pollution.