Abstract
Indium (In) is a critical metal widely used in electronic equipment, and the supply of this precious metal is a major challenge for sustainable development. The use of microorganisms for the recovery of this critical high-tech element has been considered an excellent eco-friendly strategy. The Rhodanobacter sp. B2A1Ga4 strain, highly resistant to In, was studied in order to disclose the bacterial mechanisms closely linked to the ability to cope with this metal. The mutation of the gene encoding for a DedA protein homolog, YqaA, affected drastically the In resistance and the cellular metabolic activity of strain Rhodanobacter sp. B2A1Ga4 in presence of this metal. This indicates that this protein plays an important role in its In resistance phenotype. The negative impact of In might be related to the high accumulation of the metal into the mutant cells showing In concentration up to approximately 4-fold higher than the native strain. In addition, the expression of the yqaA gene in this mutant reverted the bacterial phenotype with a significant decrease of In accumulation levels into the cells and an increase of In resistance. Membrane potential measurements showed similar values for native and mutant cells, suggesting that there was no loss of proton-motive force in the mutant cells. The results from this study suggest a potential role of this DedA family protein as a membrane transporter involved in the In efflux process. The mutant strain also has the potential to be used as a biotool in bioaccumulation strategies, for the recovery of In in biomining activities.
Highlights
Indium (In) is quite rare in nature and is found as a trace element in the earth’s crust (50–200 ppm); it is an important metal supporting modern communication and electronic industry (Alfantazi and Moskalyk, 2003)
Tn5 was located into an open reading frame encoding for a protein with a high degree of homology to a DedA family protein [National Center Biotechnology Information (NCBI) Reference Sequence: WP_108473013.1], which is a highly conserved protein family poorly characterized (Doerrler et al, 2013)
We show that mutation of DedA homolog YqaA affected drastically the In resistance, which indicates that this protein plays an important role in the In resistance phenotype of Rhodanobacter sp
Summary
Indium (In) is quite rare in nature and is found as a trace element in the earth’s crust (50–200 ppm); it is an important metal supporting modern communication and electronic industry (Alfantazi and Moskalyk, 2003). The extensive mining activities and the manufacturing of the In-based thin films used in many electronic devices often involve a significant amount of water that is discharged to sewers releasing soluble toxic metal species (e.g., GaIII, InIII, arsenite (AsIII), and arsenate) (Fashola et al, 2016) and, the widespread environmental contamination. These metal-contaminated environments are often colonized by microbial communities well adapted to these tough conditions. Several metal resistance mechanisms are known in microorganisms, such as the change of the metal redox state, metal cell impermeability, secretion of metal chelating agents to the environment, metal sorption on the microbial surface, and metal efflux (Srivastava and Kowshik, 2013)
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