Identification of three metallothioneins in the black soldier fly and their functions in Cd accumulation and detoxification

Highlights: • There are three BSFMTs in H. illucens which are rich in the gut and malpighian tubules. • Metal binding sites of BSFMTs are more than other insects. • BSFMTs expression level changed in response to Cd concentrations. • Overexpression of recombinant BSFMTs enhanced Cd tolerance in Escherichia coli. • RNAi of BSFMTs provided their function in Cd detoxification and tolerance. The black soldier fly (BSF) Hermetia illucens has a strong tolerance to cadmium stress. This helps to use BSF in entomoremediation of heavy metal pollution. Rich metallothionein (MT) proteins were thought to be important for some insects to endure the toxicity of heavy metal. We identified and characterized three MTs genes in BSF (BSFMTs), including BSFMT1, BSFMT2A, and BSFMT2B. Molecular modeling was used to predict metal binding sites. Phylogenetic analysis was used to identify gene families. Overexpression of the recombinant black soldier fly metallothioneins was found to confer Cd tolerance in Escherichia coli. Finally, functions of BSFMTs in BSF were explored through RNA interference (RNAi). RNAi results of BSFMT2B showed that the larval fresh weight decreased significantly, and the larvae mortality increased significantly. This study suggests that BSFMTs have important properties in Cd detoxification and tolerance in BSF. Further characterization analyses of physiological function about metallothioneins are necessary in BSF and other insects.