Plasmid paradox: Persistence of recombinant plasmid without antibiotic selection elevates tellurite resistance in Escherichia coli strain A1 mutant

The Tellurite (TeO32-) is a highly toxic by-product of copper refining. Microbiological tellurite reduction into elemental tellurium (Te0), a photoelectric and semiconductor metalloid used in green technologies such as photovoltaic cells and rechargeable batteries, can alleviate tellurium resource scarcity. Escherichia coli Strain A1 transformant harbors a recombinant pHSG398 plasmid (pHSG-A1) expressing a putative tellurite-reducing gene (A1-ORF1) and a chloramphenicol resistance gene (Cmr). The instability of tellurite reduction activity due to loss of recombinant plasmid when cultured in media with and without antibiotics is a major concern in the use of E. coli Strain A1 in tellurite bioremediation and tellurium recovery. The E. coli Strain A1 mutant was isolated and characterized from the parental E. coli Strain A1 transformant culture after successive cultivation in Luria Bertani (LB) medium without antibiotic-mediated selection. A1 mutant showed higher tellurite resistance in 2 mM Na2TeO3 at pH 7.0. The presence of the A1-ORF1 was validated in the A1 mutant through polymerase chain reaction (PCR) using A1-ORF1-specific primers. The exact mutations that drive the persistence of recombinant pHSG-A1 plasmid in E. coli Strain A1 mutant with elevated tellurite resistance without antibiotic-mediated selection pressure merit further investigation. Elucidating the mechanism of plasmid compensatory evolution is important in understanding the persistence of antimicrobial resistance in bacterial populations. This will also help to develop novel strategies to combat the imminent threat of antimicrobial resistance. Moreover, the identification of E. coli Strain A1 mutant with elevated tellurite resistance provides an opportunity for the efficient recovery of tellurium in the future.