Integration of transcriptomic and metabolomic reveals metabolic pathway alteration in earthworms (Eisenia fetida) under copper exposure

Copper is a trace element that necessary for plant growth in the soil. However, in recent years, due to human activities, the content of copper in soil exceeds the standard seriously, which is threatening the safety of soil animals, plants and even human beings. In this study, we investigated the effects and molecular mechanisms of 60 days long-term copper exposure on earthworms (Eisenia fetida) at 67.58 mg/kg, 168.96 mg/kg and 337.92 mg/kg concentration by using transcriptome and metabolomics. Transcriptome analysis showed that the expression of energy metabolism related genes (LDH, GYS, ATP6N, GAPDH, COX17), immune system related genes (E3.2.1.14) and detoxification related genes (UGT, CYP2U1, CYP1A1) were down-regulated, the expression of antioxidant system related genes (GCLC, HPGDS) were up-regulated in copper exposure experiment of earthworms. Similarly, metabolomics analysis revealed that the expression of energy metabolism related metabolites (Glucose-1-phosphate, Glucose-6-phosphate), TCA cycle related metabolites (fumaric acid, allantoic acid, malate, malic acid) were down-regulated, digestion and immune system related metabolites (Trehalose-6-phosphate) were up-regulated. Integrating transcriptome and metabolomics data, it was found that higher antioxidant capacity and accelerated TCA cycle metabolism may be an adaptive strategy for earthworms to adapt to long-term copper stress. Collectively, the results of this study will greatly contribute to incrementally understand the stress responses on copper exposure to earthworms and supply molecular level support for evaluating the environmental effects of copper on soil organisms.