Ex-situ induction of Metallothionein gene in Lybiodrilus violaceous post cadmium and zinc exposure

Abstract

BackgroundEarthworms are good indicators used in evaluating the health status of the terrestrial ecosystem and metallothionein (Mt) is a biomarker monitored during environmental studies. There is however a dearth of information on metallothioneins in African earthworms. Libyodrilus violaceous is a West African earthworm well investigated and reported including its tolerance to metal pollution but the presence of Mt gene in L. violaceous is not established. MethodsThe presence of Mt. in L. violaceous was determined to validate its potential role in metal tolerance. L. violaceous sampled from Ije-Ododo soil were exposed to varying concentrations of Cadmium (Cd) and Zinc (Zn) in a potted experimental set-up and the metallothionein (MT) expressions were determined. The presence of Mt gene and metallothionein expression were determined using whole transcriptome sequencing and real-time polymerase chain reaction (PCR), respectively after extracting Ribonucleic acid (RNA) from samples on the 1 st, 3rd and 7th days. The genetic relationship of the detected MT protein sequence was compared to existing MT protein sequences and a phylogenetic tree was constructed. ResultsWe established the presence of the MT gene and the phylogenetic tree showed that it had a relationship with other earthworms' MTs. Up-regulation of Mt. expression was observed on the 7th day in L.violaceous exposed to concentrations of Cd and Zn. ConclusionOne of the modes of survival of L. violaceous to metal pollution is by the up-regulation of metallothioneins. This earthworm metallothionein protein sequence is the first report of species in the Eudriloides family and the first report in African earthworms deposited in the GenBank repository for reference. The use of L.violaceous for Cd and Zn remediation in soils could be exploited.