Can biotechnology solve environmental problems?

A transgenic organism is one to which one or several genes have been introduced, through biotechnology, that allow it to carry out functions that an organism of the same species but without those genes —which we call, by opposition, an isogenic organism— cannot perform. . Those used in agriculture are well known : the controversial herbicide-resistant corn, varieties of rice whose grain produces vitamin A, or even the cotton with which banknotes are made in the European Economic Community, are all transgenic. There has also been occasional talk of transgenic farmed salmon , capable of growing much faster and with less food than isogenic salmon; or of those transgenic bacterial cultures that are used to produce medicines or health products such as human insulin , or transgenic wheat suitable for coeliacs .

However, biotechnology has the potential to do much more. Transgenic forms of mosquitoes have been developed that help control the pests of these insects, and with them, the associated diseases. There are already purple tomatoes that, thanks to snapdragon genes, can synthesize substances with anti-cancer properties. And of course, transgenesis can also be used to fix environmental damage.

On the day of the International Commitment against Mercury , we will talk about how biotechnology can help decontaminate and recover environments devastated by the contamination of this heavy metal.

A key concept: bioremediation

Bioremediation is defined as the use of living beings or their derived products to recover a natural environment disturbed by pollutants. For this, microorganisms, plants or enzymes capable of degrading or, at least, removing and retaining from the natural environment those chemical compounds that cause the negative impact are usually used, whether in the soil, in the sediments, in the mud or in the sea. .

Thus, there are three forms of bioremediation: microbial , which uses bacteria and other microorganisms; enzymatic degradation , which uses enzymes to digest contaminants, and phytoremediation , using algae, fungi, or plants.

We all have the sad memory of what happened in 1998 in Aznalcóllar, Seville, after which the soils of Doñana were contaminated with mercury and other heavy metals for years. For this type of situation, the best option is phytoremediation , specifically using plants. Although it is the slowest method of the three, it is also the one that allows action on large surfaces at low cost, and plants have a greater capacity to penetrate deep layers of the soil than microorganisms. But we found a problem: we do not know of any plant capable of removing mercury from the soil and retaining it in its tissues . In general, mercury is extremely toxic to plants.

GMO plants that eat mercury

In nature there are bacteria that are capable of absorbing and metabolizing mercury. We found this ability in a good number of different species of the genera Streptomyces, Pseudomonas and Bacillus. These bacteria have a complex enzyme system that allows them to perform these feats and is controlled by several genes. Some allow mercury to be absorbed and reduced ; others are involved in the conjugation of mercury into organic forms ; others in the transport of mercury to the interior of the cell ; others code for proteins that allow mercury to be attached to the cell membrane without causing damage… but we are talking about bacteria. As indicated, we know of no plant capable of doing this. But what happens if we get those genes and put them into a plant ?

Initially, transgenic varieties of plants capable of absorbing mercury, reducing it and transforming it into a volatile form were designed, which diffused into the atmosphere, thus decontaminating the soil. Now, although it is true that volatile mercury is much less toxic, there is always the risk that it will precipitate again and contaminate new regions.

In the next step, new genes were incorporated that made it possible not only to absorb mercury from the soil through the roots and transport it to the aerial parts of the plant , but also to chelate mercury and accumulate it in the vacuoles, in a mercury-polyphosphate complex. This system has a couple of additional advantages over the volatilization method. The first, which allows mercury to be retained in a controlled place , such as inside plant tissues, instead of volatilizing into the atmosphere, without poisoning the plant. The second advantage is the possibility of collecting the plants and extracting the retained mercury , in a controlled manner.

With this outline, as an example, it is easy to glimpse the enormous potential that biotechnology can have in the field of bioremediation . What seems more unpredictable is the reaction of those groups that are radically opposed to transgenesis, knowing that it can be a very effective tool to solve many and very serious environmental pollution problems.

REFERENCES

Priyadarshanee, M., Chatterjee, S., et al. 2022. Cellular and genetic mechanism of bacterial mercury resistance and their role in biogeochemistry and bioremediation. Journal of Hazardous Materials, 423, 126985. DOI: 10.1016/j.jhazmat.2021.126985

Rylott, E. L., & Bruce, N. C. 2020. How synthetic biology can help bioremediation. Current Opinion in Chemical Biology, 58, 86-95. DOI: 10.1016/j.cbpa.2020.07.004

Schiering, N., Kabsch, W., et al. 1991. Structure of the detoxification catalyst mercuric ion reductase from Bacillus sp. strain RC607. Nature, 352(6331), 168-172. DOI: 10.1038/352168a0

Xu, S., Sun, B., et al. 2017. Overexpression of a bacterial mercury transporter MerT in Arabidopsis enhances mercury tolerance. Biochemical and Biophysical Research Communications, 490(2), 528-534. DOI: 10.1016/j.bbrc.2017.06.073

Yaashikaa, P. R., Kumar, P. S., et al. 2022. A review on bioremediation approach for heavy metal detoxification and accumulation in plants. Environmental Pollution, 119035. DOI: 10.1016/j.envpol.2022.119035