Team:Rice/Future Directions
FUTURE DIRECTIONS
Kill Switch Improvements
One problem that might be encountered in real life application of the chromium remediation bacteria is the failure of the kill switch due to mutations introduced during DNA replication. Because the kill switch is nonessential, there is no selective pressure to retain the kill switch. In fact, because the kill switch circuit contains a gene for a toxin, leaky expression of the toxin introduces selective pressure to make the kill switch nonfunctional. This is troubling because the failure of the kill switch means that synthetic organisms could be left uncontained in the environment. Work may be done to ensure that the kill switch genes stay unaltered. One stable kill switch design to consider is detailed here
Work may also be done to fine-tune the concentration of chromium at which the kill switch activates. Since chromium levels in water are low, it is possible that the kill switch may activate before the bacteria have reduced the level of Cr(VI) to the desired level. Alternately, the bacteria may be too sensitive to chromium and not activate the kill switch at all. Experiments to determine at what concentration of chromium the kill switch activates can be done to verify whether the chromium reducing bacteria respond in the correct manner. If the bacteria activate the kill switch too soon, a signal amplification circuit to increase the bacteria’s sensitivity to chromium can be incorporated, and if the bacteria activate the kill switch too late, modification may be done to the chromium sensitive promoter used in the kill switch and chromium remediation circuits.
Sequestration of Chromium
In addition to reducing Cr(VI) to Cr(III), we may consider ways the chromium remediation bacteria may sequester the Cr(III) from the environment, in order to prevent the oxidation of Cr(III) to Cr(VI).
Modification of Chromium Remediation Circuit for Use in Shewanella oneidensis
E. coli does not grow particularly well in wastewater, where our chromium remediation system is intended to work; it is likely to be outcompeted by other microbes. To avoid this, we could move our chromium remediation circuit to Shewanella Oneidensis, an anaerobic gram-negative bacterium that thrives in wastewater conditions. Our chromium remediation circuit must be modified so that promoters, RBSs, and other plasmid components that function in E. coli also function in Shewanella.
