GM plants that detect landmines

Hugh Warwick comment on superweed study:

this is a very limited study which does nothing to address the very real concerns that have been expressed for years. It is also rather revealing that the results are only emerging well after gm crops have been released into the wild .... would the data have been published if it had shown different results?? best wishes Hugh
---

Instead of operating in such a way that we don't endanger other species, we'll just clone them as they disappear. Instead of transforming, or at least reducing, our negative global impacts, we'll just try and amerliorate them with hi-tech fixes which bring their own added level of complexity and hazard.

Thanks to Stokely Webster for this, including apposite comment
---

Dear all

...how depressing that, not satisfied with their already invidious contamination of the world, the military and dirty industry proposes another breath-taking fix to symptoms they themselves perpetuate. I can imagine the glowing landscape now (our friend the lux gene figures).

Chief quote: While their potential for improving crops plants is important, environmental monitoring is an area where GM plants can perform a crucial role in a low-impact manner, a role that even GM opposition would be hard-pressed to criticize ... GM plants could be used as biosensors to monitor radioisotope levels around nuclear power plants, or to detect jet fuel contaminants at military bases. They could also disclose the presence of certain other unwanted and especially dangerous substances in our environment of which presently there is no good way of monitoring. One of these is buried explosive devices.
---

Plants that detect landmines, and other biosensors
ISB News Report, by C. N. Stewart & S. K. Wheaton
Information Systems for Biotechnology, USA,
This email address is being protected from spambots. You need JavaScript enabled to view it.
DATE: February 2001
archive: http://www.gene.ch/genet.html

The furor over genetically modified (GM) plants has focused on crops with engineered agronomic qualities, such as insect resistance and herbicide tolerance. Critics are primarily concerned with food safety issues and ecological consequences. But GM technologies have much further ranging applications than simply agriculture. While their potential for improving crops plants is important, environmental monitoring is an area where GM plants can perform a crucial role in a low-impact manner, a role that even GM opposition would be hard-pressed to criticize.

It is possible that in the near future, GM plants could provide constant, landscape-level data on environmental hazards. Current monitoring of surface and sub-surface contaminants, both inorganics such as heavy metals and organic toxins such as PCBs, relies on frequent water sampling of wells, an expensive and labor-intensive task. GM plants could be used as biosensors to monitor radioisotope levels around nuclear power plants, or to detect jet fuel contaminants at military bases. They could also disclose the presence of certain other unwanted and especially dangerous substances in our environment of which presently there is no good way of monitoring. One of these is buried explosive devices.

Several laboratories are currently performing research using plants as biosensors. This entails the isolation of specific inducible promoters (gene switches) that can be fused to one or more genes encoding a visible marker. The current visible marker of choice is green fluorescent protein (GFP) from the Pacific jellyfish (Aequorea victoria). GFP has the unique property of fluorescing green when excited by blue or UV light. A DNA construct containing a specific inducible promoter could be fused to GFP and then transferred into a plant for biomonitoring. For example, in a case where the promoter has been isolated and modified so that it is responsive to copper(1), plants containing this construct might be deployed around the periphery of a copper mine to monitor copper movement into the surrounding countryside. When copper was present in sufficient concentrations to trip the promoter, plants would fluoresce green at that location. Ultimately biosensors of nature could be used in conjunction with bioremediators, the perfect marriage being that where an individual plant performs both functions.

The application we want to consider here is the detection of buried explosive devices, such as landmines. Landmines generally have small plastic housings of extremely inexpensive construction that contain trinitrotoluene (TNT) or other explosives. Landmines come in various sizes and shapes and are, for the most part, designed to explode and maim whatever steps on the soil surface covering the mine. Cambodia, Angola, and Pakistan are examples of countries that are littered with landmines deployed by invading military, government, and/or rebel groups. Most of the nations in this situation are those whose economies rely heavily on non- automated agricultural production, and the presence of landmines effectively removes large areas of arable land from agricultural production. The more obvious and urgent problem is that these mines kill and maim multiple people everyday. Those who live in the vicinity of minefields are normally aware of the existence of the minefield itself, but not of the specific locations of the mines that may be planted randomly as little as 10 meters apart. Since they are plastic, landmines cannot be located by metal detectors; in the developing world, the most common de- mining practice is that of a man with a stick. He will search for a landmine by feel, a practice that is imprecise at best and often a hideous short-term career at its worst.

The idea to use organisms to detect TNT was first exemplified using GM bacteria by Dr. Robert Burlage and his coworkers at the Oak Ridge National Laboratory(2). Their bacteria, Pseudomonas putida, had a TNT inducible promoter fused to GFP and were tested on a faux minefield with surrogate landmines. Pseudomonas putida detected five of five landmines in a one- quarter acre plot; however, they also produced two false positive signals, indicating the presence of a landmine where none existed. There are several other drawbacks to a bacterial-based system. It requires that bacteria be grown and sprayed onto the minefield, which could be determined to be environmentally unacceptable. A government also might well object to the release of recombinant bacteria in the interest of national security. Additionally, it has been found that the bacterial signal is dependent on a plant substrate for bacterial colonization. A plant-based detection system has the advantage of utilizing a macroscopic, and trackable, organism; TNT would be absorbed by plant roots and then transported to leaves(3) where the fluorescence could be readily observed. The root structures would also more effectively mine the soil for trace explosive, resulting in increased mapping accuracy. Another advantage is that the plants used could be optimized for specific ecological conditions.

How would such a plant-based TNT detection system work? The first step would be sowing detector plant seed over a minefield in a manner that would result in uniform coverage, a potential logistical problem that would require helicopter-based seed pelleting. A homogeneous stand of plants would need to be established so the roots could cover the mine-leachate soil volume. It would be necessary to supply plants with water and nutrients via a helicopter to assure they will be in good health with normal protein production. Finally, plants would need to be detected. Simply, the plants located over a landmine would fluoresce green; those not in the proximity of a mine would not fluoresce. The false positive signals in the bacterial system were due to leaching(2); a plant-based system, where the promoter is tripped by an accumulation of TNT, should not be nearly as vulnerable.

An important component of any detection system is the photonic device used for picking-up the fluorescent biosensor signals. At our laboratory in North Carolina, we work at ground level in the dark using a strong UV lamp to shine on GFP-producing plants. Obviously, this practice is not transferable to a field situation where it becomes far too reminiscent of the man with the stick. In another National Laboratory in Santa Barbara, John Di Benedetto and his colleagues have produced laser-induced fluorescence imaging (LIFI) and laser-induced fluorescent spectroscopy

(LIFS) devices that can be used to detect and measure fluorescence from a stand-off(4). Scaling remote sensing to airborne devices is critical for the successful detection of biological-based landmine detection systems and other real-time biosensors. Says Dr. Di Benedetto, "(Airborne) laser- induced fluorescence will provide remote access and direct evidence of specific contamination, whether it is TNT, heavy metals, or pathogens. It will bring a whole new dimension to remote sensing."

The uses of biotechnology will increasingly move from the agricultural and medical toward environmental applications. A number of research groups in both the public and private sectors are working to make environmentally useful GM organisms a reality. We believe the wholesale environmental objection to GM plants will be moderated by landmine-detecting GM plants, as well as other explicitly environmentally useful GM plants. A biotechnology that can monitor the presence of environmental contaminants, and then possibly even clean them up, has the potential to replace expensive extant technologies. For example, plants that can bioremediate mercury have already been developed(5). These plants have the ability to absorb and convert toxic forms of mercury to less-toxic elemental mercury that they subsequently volatilize, and a mercury-inducible GFP marker would be a useful addition. Biotechnology can and should play a pivotal role in monitoring toxins and in cleaning up the environment. A GM plant that detects the location of landmines seems like a biotechnological advance that even Prince Charles could love.

Sources: 1. Mett VL, Lochhead LP, and Reynolds PHS. 1993. Copper-controllable gene expression system for whole plants. Proceedings of the National Academy of Sciences USA 90(10): 4567-4571. 2. Burlage RS. 1999. Green fluorescent bacteria for the detection of landmines in a minefield. Abstracts of the Second International Symposium on GFP, San Diego, CA. 3. French CE, et al. 1999. Biodegradation of explosives by transgenic plants expressing pentaerythritol tetranitrate reductase. Nature Biotechnology 17(5): 491-494. 4. Di Benedetto J. 1999. Laser-induced fluorescence remote sensing. Abstracts of the Second International Symposium on GFP, San Diego, CA.

5. Bizily SP, Rugh CL, and Meagher RB. 2000. Phytodetoxifica-tion of hazardous organomercurials by genetically engineered plants. Nature Biotechnology 18(2): 213-217.

C. Neal Stewart, Jr. University of North Carolina at Greensboro and Transgreenix Corporation This email address is being protected from spambots. You need JavaScript enabled to view it.

Sarah K. Wheaton University of Rhode Island