The metal scavenger with a vertical gas drive is a modular system which contains five modules that are interchangeable; the transporter, an accumulation protein, a regulated promoter, a regulator and the gas vesicle cluster. The transporter imports the metal ion of choice. An accumulation protein facilitates accumulation of metal ions and prevents the cell from dying of metal toxicity. The imported metal ion also acts as a regulator for the metal sensitive promotor which activates the expression of the gvp-cluster. Thereby the recombinant bacterium with this system, accumulates metal and upon accumulation starts to float. Many applications are possible once the correct modules are selected. Water and sludge cleaning or mining of rare metals are some examples. Also the ethical concerns of these applications should be considered.

Water Cleaning

Bacteria which accumulate metal ions can be used to remove toxic metals or other contaminants from ground or surface water. This microbial system is described for scavenging of arsenite, copper and zinc. An example where removal of arsenic from subsoil water by this organism could prevent serious poisoning of millions of people. In Bangladesh and other countries over ten million water pumps where installed, to improve personal hygiene but this raised a new problem. The unforeseen consequence was that, because the ground water level dropped dramatically and the arsenic contamination in the ground water began oxidizing. Chronic consumption of this water will lead to arsenic toxification. Arsenic causes swears caused necrosis of cell tissue because of disruption of the ATP production (wikipedia). To prevent more people from arsenic poisoning, the arsenic concentration can be decreased by bacteria (containing the system as described before) and subsequently filtering these bacteria from the water, it can be consumed by individuals. Arsenic is most prominently found in sub-soil water found as As(III) (anaerobic condition) and as As(V) in surface water (mildly aerobic condition). For humans the trivalent state was found to be most toxic. This is exactly the state which is most efficiently bound by fMT and transported by GlpF.

Sludge Cleaning

Due to application of sewage sludge and industrial sludge into environmental soil, toxic metals accumulates in river sludge and soil. This contaminated soil is usually "diluted" with uncontaminated soil to decrease the concentration of metals below the maximum allowable concentration (10ppb (µg/L)). But by consumption of vegetables cultivated on these soil or meat from cattle that pastured on these fields, the concentration of these toxic compounds will increase in higher organisms. A bacterium that is able to absorb and encapsulate metals and that floats, would be able to separate the metals and the sediment. It would be enough to simply put the bacteria and the sediment in large container stir them together and let the cleaned sediment sink and scoop of the floating metal filled bacteria. Such a purification plant would look similar like the sewage disposal plants that we use today. Simply inject the bacteria in the sediment, the bacteria full of metals will start floating to the surface and they can readily be collected by floaters, such as the ones which are now used to collect oil pollution from the sea.


Due to the huge worldly consumption of crude oil there is a high probability that the fossil oil reserves will be exhausted within several decades, but this is not only the case for oil, also the reserves of rare metals are becoming less abundant. Therefore the mining yield should be increased to get as much of the desired metal out of the ore as possible. For mining of copper and gold a metal oxidizing bacteria species called, Thiobacillus ferrooxidans is already being used for over 10 years. This bacterium gains energy by oxidizing insoluble sulfides of metals like copper, gold, lead, zinc, nickel and even uranium to soluble sulfides. This causes an improved recovery (Rawlings 1994), but to increase the yield and specificity a genetically engineered system could be used. Therefore a robust bacterium like the thermophilic Thermus thermophilus or the radiation resistant Deinococcus radiodurans (or a species which allows easier clonig) could be used. The transporter and metallothionein for specific import and sequestering of the rare metal, should be overexpressed. For these low concentrations the kock-out of the exporter of that metal would be required. But then finally, what keeps us from mining gold from the oceans or deserted mines to collect what was first impossible to extract!?

Ethical concerns

One of the most prominant ethical issues surrounding the application of genetic modified organisms is safety.The application should not be an environmental hazard by itself nor should it be a hazard for human health. Using a confined disposal plant would for most part prevent the spread of genetically modified bacteria into the environment, however, in case of heavy rain the basins can overspill which allows the bacteria to enter the environment. So only a confined basin is not enough, a self-destruction plasmid, which induces cell death after a certain time, should be added as well. In that case, even if the bacteria accidently end up outside the confined disposal plant, they will die after a while and will be unable to spread or transfer their DNA. This death plasmid should be carefully choosen since the bacteria need time to clean the water, sludge or mine the metals. Read more on safety and ethical issues...