Isolation of heavy metal resistant Staphylococcus epidermidis strain TWSL_22 and evaluation of heavy metal bioremediation potential of recombinant E. coli cloned with isolated cadD.

A heavy metal resistant bacterial strain, TWSL_22 was isolated from an industrial effluent sample and tested for heavy metal tolerance and resistance. The strain was molecularly characterized as Staphylococcus epidermidis based on 16S rRNA gene analysis and the sequence was deposited in the NCBI repository (Accession number KT184893.1). Metal removal activity (P < 0.001) of TWSL_22 was 99.99 ± 0.001%, 74.43 ± 2.51% and 51.16 ± 4.17% for Cd, Pb and Cu respectively. Highest MIC was observed for Cd. Antibiotic susceptibility assays revealed the strain TWSL_22 to be resistant to several antibiotics. The strain was screened for possible heavy metal resistant genes and presence of cadA, copA and cadD was confirmed by PCR. A DNA fragment containing complete sequence of cadD (618 bp) was isolated and cloned into pET 21a(+), transformed into E. coli BL21 and designated as E. coli/cadDET. E. coli/cadDET showed high metal tolerance capacity and could remove over 82% of heavy metals (Zn2+, Cd2+, Cu2+, Cr3+) in the industrial effluent.