Metallothionein expression and Neutral Red uptake as biomarkers of metal exposure and effect in Eisenia fetida and Lumbricus terrestris exposed to Cd

In this study we compared short-term, sub-lethal responses of two different earthworm species, Eisenia fetida and Lumbricus terrestris, exposed to Cd (100 mg/kg) under laboratory conditions. Biological responses at the cellular and molecular genetic levels of organisation were measured. First, the Neutral Red uptake test was performed on extruded coelomocytes. Observations showed a significant reduction in cell membrane integrity in E. fetida exposed to Cd, whilst L. terrestris membranes appeared to be unaffected. Second, metallothionein 2 (MT2) gene expression levels were measured by Q-RT-PCR. Observations showed a significant up-regulation of the Cd-inducible metalloprotein in both species. Transcriptome measurements indicated that basal MT gene expression levels were higher in E. fetida than in L. terrestris, but Cd-induced MT2 up-regulation was approximately similar in samples from the two species. In conclusion, the susceptibility of coelomocyte membranes to Cd-evoked toxicosis is not correlated with Cd-induced MT2 expression levels.