User:FlorianA

From 2013.igem.org

Phytoremediation

What it´s all about

Figure 1: Plants can internalize pollutants dissolved in water [1].

Today science and technology are eager to protect the environment from further harm and reverse the damage already done. Of these technologies, bioremediation and phytoremediation in particular, seem to be the most promising ones as they try to help nature help itself. Bioremediation is defined as "the process of judiciously exploiting biological processes to minimize an unwanted environmental impact; usually it is the removal of a contaminant form the biosphere." [Prince, 2000] Phytoremediation is the concept of removing pollutans either directly by plants themselves or by specialized bacteria living in a symbiosis with plants. There is a multitude of different pollutants that are primary targets for remediation such as Polychlorinated biphenyls (PCBs), insecticides such as dichlorodiphenyltrichloroethane (DDT), heavy metals such as cadmium or mercury or pharmaceutical products such as macrolide antibiotics, diclofenac or ethinylestradiol.

Phytoremediation vs. Bioremediation

**Table 1:** Costs of different techniques for soil remediation.
Type of treatment	Range of costs, $/ton
Phytoremediation	10-35
In situ bioremediation	50-150
Soil venting	20-220
Indirect thermal treatment	120-300
Soil washing	80-200
Solidification/stabilization	240-340
Solvent extraction	360-460
Incineration	200-1500

So why did we choose Phytoremediation over the approach of classical Bioremediation using bacteria like so many iGEM-teams do?
There are several reasons that led to our decision. Firstly, we thought that the overall applicability of plants is much higher than that of bacteria. Provided a sufficient safety mechanism transgenic plants can be deployed almost everywhere. All they need is light and they will sustain themselves. Bacteria on the other hand are harder to contain and are generally more expensive than plant systems concerning maintenance costs.

Considering all these factors, we decided that Phytoremediation was the way to go. And thanks to all the fantastic work of other iGEM-teams in previous years we had the possibility to choose from a wide variety of existing BioDegradation bricks!
Our main goal in this project was to use the excellent existing bricks and build upon the work of previous teams but to improve their applicability by establishing a completely new chassis.

Standing on the Shoulders of Giants

As we established our idea we investigated several remediation projects done by previous teams to look for ways to improve them or even come up with a totally new approach. Looking through interesting projects like those of Bielefeld 2012, Imperial College London 2010 and of course the algae project of Bilkent UNAM Turkey, we noticed that there have only been a few phytoremediation projects in the iGEM competition. We thought there could be a more suitable chassis for remediation and stumbled upon the well established model organism Physcomitrella patens. As nobody in our team had ever worked with moss (or with plants for that matter) we had a lot of research to do. As there was nobody working with this organism at our whole university we had to look for other universities to find some experts we could win as an advisor for our team. Thankfully Prof. Reski´s homepage provided the necessary papers, methods and details and he was also willing to support our project. Having looked into it, we were conviced that this plant is what we have been looking for and that it would be great to introduce it to the iGEM community.

**Table 2:** Previous remediation projects
Team	Year	Organism	Description
Peking University	2010	E.coli	Heavy metal decontamination of aquatic environments via binding proteins
UT Dallas	2010	E.coli	Establishing E.coli as a biosensor for environmental pollutants using fluorescence
METU Turkey	2010	E.coli	Designing a biosensor to detect CO as a dangerous pollutant
USeoul Korea	2010	E.coli	Using fluorescence proteins to detect various heavy metals in water
TU Delft	2010	E.coli	Enabling hydrocarbon degradation in aqueous environments
Michigan	2009	E.coli	Sensing and degrading toluol
UQ Australia	2009	E.coli	Uptake and reduction of mercury in water
Cornell University	2009	B.subtilis	Creating a cadmium sensor

Seeing all those great projects we decided not only to improve biodegredation by looking at the actual degredation processes but more importantly by establishing a wholly new chassis to the iGEM competition and to phytoremediation in general.

Why Physco, why?

So why exactly did we choose Physcomitrella patens as the basis for our remediation project? One big point was that we wanted to make our filter system available for everyone and bacteria just didn´t do the trick for us: Harder to contol, harder to grow and harder to implement. We wanted something that could be deployed in a few simple steps and would be self-sustainable and self-renewing. Short, we wanted an autotrophic organism which could be easily established in an aquatic environment. Not only does our moss provide us with these features as it only needs water, light and carbon dioxide to grow and can be grown on soil as well as in water but it can also be easily cultivated in bioreactors which gives us the possibility to envision industrial scale waste-water treatment based on our system. For more information on Physcomitrella patens you can read through the Physcomitrella patens wiki page.

Constructed Wetlands as a large-scale application of Phytoremediation

In the last decades Phytoremediation made the transition from a solely scientific approach to an industrial scale water treatment technique. Today large amounts of water are treated through constructed wetlands as it poses one of the simplest and most cost-effective ways to treat sewage-waters either on their own or in symbiosis with a traditional treatment plant.

How do they work and why do we need them?

Figure 2: Constructed wetland diagram. [2]

Natural wetlands, as well as constructed ones, are systems in which plants and microorganisms form complex biotopes capable of filtering, degrading or inactivating various substances in the water. The wetland, slowing the speed of the passing water, can trap suspended solids in the vegetation which also accumulates pollutants by absorbing them. As these wetlands are a perfect habitat for microorganisms various degredation processes take place ridding the water from a variety of pollutants.

Figure 3: Constructed wetland plant [3]

Higher environmental standards in first world countries as well as the growing industrialization have led to a skyrocketing demand in sewage water treatment. The capacities of traditional treatment systems have shown to be ineffective and too expensive. Constructed wetlands pose a real alternative to conventional technologies as they are not only reliable and cost-effective but the most natural and environmental friendly way of cleaning water. They leave no waste behind, are self-sustaining and have no demand for artificial energy. Other than most other environmental measurements constructed wetlands are very attractive for businesses as they are cheap alternatives to existing systems rather than costly additions.

References:

[Prince, 2000] Prince, R. C. (2000). Bioremediation. Kirk-Othmer Encyclopedia of Chemical Technology.

EPA Homepage

Guardian 01.11.2011 "Plants working to combat pollution. Examining phytoremediation – using plants to mitigate pollution." The Guardian article.

G.Kvesitadze: Biochemical Mechanisms of Detoxification in Higher Plants, Springer-Verlag, Heidelberg 2006

EPA(2001) Brownfields technology primer: selecting and using phytoremediation for site cleanup, pp1-24