Batteri geneticamente ingegnerizzati per il biorisanamento da metalli pesanti: approcci recenti

The rapid technological development is leading to the worldwide accumulation of large quantities of electronic waste. Electronic waste management has many thorns due to its enormous volume, complexity of components and potential toxicity. The scientific community is engaging in the search for eco-friendly disposal of electronic waste also allowing the recovery of the metals present in them. Among the more sustainable alternatives to chemical remediation, biologically assisted degradation represents a sustainable, cheaper, less detrimental and applicable option. The cell-surface display (CSD) technology is among the most promising biological approaches developed for this aim. Such a technology is based on microbial biosorption, a process based on the presence of cell surface molecular complexes capable of capturing metal ions for heavy metal detoxification. Movel biotic‐abiotic co-assemblies suitable for the removal of cadmium and lead at high efficiencies have been constructed by genetically engineering Escherichia coli BL21 cells to display the heavy‐metal‐capturing fusion protein on their cell surface and using magnetic nanoparticles (MNPs). The co-assemblies maintained high heavy-metal-removing efficiency at different pH values or at different ion concentrations of a broad spectrum of heavy metals, including Hg2+, Cu2+, Cr3+ and Ni2+. The CSD technology has also been used to develop an engineered whole-cell detection system based on the activation mechanism of the regulatory metalloprotein MerR of the mer operon using the CSD technology. In the presence of mercury, the mercury-dependent transcription factor MerR de-represses the transcription of genes involved in the mechanisms of mercury detoxification, such as the merA structural gene, coding for a mercuric reductase capable of reducing Hg2+ to Hg0 mercuric reductase encoded by the merA structural gene. Two biochemical systems, respectively aimed at the bio-detection and bioremediation of mercury, have been generated by replacing the structural genes of the mer operon respectively with the gene encoding for the mercury reductase MerA and the bio-sensing protein mCherry, and transforming the resulting construct into Escherichia coli DH5α cells. The genetic sequence encoding for the extracellular portion of the outer membrane protein OmpA was included in the two genetic constructs to display the functional groups of the mercury reductase enzyme MerA or the mCherry protein on the microbial cell surface. In this way, the mercury in the medium can be effectively and directly monitored and reduced without the need of importing it in the cell.