At Scrannase Systems we have developed an effective microbial bioremediation strategy to remove the toxic mercury(II) species (Hg2+) from heavily polluted environments in situ (directly on site).
We successfully engineered the well characterised bacterium Escherichia coli such that it can: (i) tolerate high concentrations of environmental Hg2+, (ii) move along Hg2+ gradients to localise at regions of the highest concentrations, and (iii) express bioremediative genes in the presence of Hg2+ to remove it from the environment.
Our Solution
For microorganisms to be suitable bioremediative tools they must confer resistance to the toxic species they are targeting for remediation. In nature, to tolerate toxic chemical species, organisms possess genes that encode proteins to effectively remove these species from the cellular environment (either by actively pumping them out, converting them to non-toxic forms or sequestering them) so that they cannot cause damage to the cell. These genes can be characterised and then engineered into microorganisms that aren’t naturally resistant, allowing them to survive in these normally inhospitable environments.
To achieve Hg2+ resistance, our selected E. coli strain was transformed with a constitutively active (constantly expressed) operon containing the phytochelatin synthase (PcPCS1) gene and the merB gene. Phytochelatin synthase is an enzyme that catalyses the synthesis of intracellular phytochelatins – small oligopeptide chelators – which have a high affinity for Hg2+. Upon Hg2+ entrance into the recombinant E. coli cells (i.e. in Hg2+ polluted environments), phytochelatins coordinate with Hg2+ – alleviating its toxic effect. The merB gene encodes an intracellular organomercurial lyase which catalyses the release of Hg2+ from highly toxic mercury containing organic compounds (also found in Hg2+ polluted environments). Liberated Hg2+ ions are then sequestered by vacant phytochelatins inside the cell, maintaining the toxic-free intracellular environment.