How Plants and Bacteria can Clean the Earth

Have you ever seen black smog come out of cars? Or noticed an unnatural oily film on water puddles in parking lots? Humans have polluted practically every corner of our planet and most of it is invisible to our eyes. Sadly, Earth suffers the consequences of this pollution. But scientists have recently found a simple way to restore contaminated soils back to health. In this article, we will talk about how plants and bacteria team up to restore our polluted world!

Have you ever seen black smog come out of cars? Or noticed an unnatural oily film on water puddles in parking lots? Humans have polluted practically every corner of our planet and most of it is invisible to our eyes. Sadly, Earth su ers the consequences of this pollution. But scientists have recently found a simple way to restore contaminated soils back to health. In this article, we will talk about how plants and bacteria team up to restore our polluted world!

WHAT IS REMEDIATION?
Years of irresponsible human activities have caused our planet to become polluted with harsh chemicals. Once these chemicals settle into the earth, it is very challenging to remove them. These pollutants pose a huge threat to the health of humans and wildlife. Trichloroethylene (TCE) is a long-lasting chemical pollutant that has What are we doing about this problem? One popular method is excavation, in which contaminated soil is literally dug out of the ground with big construction machines. If the groundwater, the water layer below the soil surface, is polluted, pumps are used to pull the water out and treat it. These methods are very expensive.

BACTERIA HELP PLANTS CLEAN UP THE ENVIRONMENT
How can a tiny bacterium be of help to a big tree? Well, scientists discovered a very special type of bacteria known as an endophyte. But what about our TCE problem? A special bacterial endophyte known as PDN was used because it came from poplar trees and could grow in super-high levels of TCE [ ]. The bacteria PDN was tagged green (Figure ) so scientists could use a special microscope to verify that the endophyte could enter the plant. The next step was to get the PDN into poplar trees. This was done by simply soaking some poplar sticks in a bucket of bacterial solution. Then the sticks were poked into the ground of a TCE-polluted site. Another group of sticks, called controls, were also stuck into the ground, but were not added to the bacterial solution. By monitoring the trees with PDN and the control trees, biologists could see if PDN helped the trees clean up the TCE pollution. Look at the photograph in Figure . Do you think the bacteria helped the trees? week after being added. These images, taken using a special microscope that can detect green fluorescence, show that the endophyte can enter roots through the cracks where roots join each other and can begin to live within the poplar tree [ ].

Figure
In this photograph, you can see how much larger and healthier the trees with PDN looked, after just year of growth. The control and PDN -containing trees were planted in alternating rows. These results also demonstrated that the endophytes did not move from one tree to another, because the control trees did not benefit from the endophytes.

WHAT IS ENDOPHYTE-ASSISTED PHYTOREMEDIATION?
We see that the trees with the added endophyte bacteria clearly look bigger and healthier than the control trees without PDN . But did those bacteria help solve the TCE problem? Scientists collected several lines of evidence showing that the bacteria-tree partnership worked. The groundwater downstream of the trees had almost no trace of TCE years after the trees were planted. So, the trees took up the polluted water but they did not look sick like the control trees did. The scientists checked inside the trees and learned that the trees given PDN had less TCE in their tissues than the control poplars had. This means that TCE taken up by the trees was destroyed inside the trees with the help of their endophyte friend. When TCE is broken down, chloride is released (since TCE is tri-chloro-ethylene). Sure enough, there was lots of extra chloride in the soil around the PDN trees.
In other words, the endophytes helped the poplars reach more TCE and break it down. This process, in which plants and endophytes work together for restorative purposes, is called endophyte-assisted phytoremediation.

ENDOPHYTE-ASSISTED PHYTOREMEDIATION
The use of endophytes to help plants remove pollutants. Now we know the bacterial endophyte helped the poplar trees fix the TCE pollution problem, but scientists still wonder exactly how it works. Since the bacteria by itself can break down TCE really well, we know that the endophyte has special enzymes to do this. But endophytes also bring many benefits to their host plants, all of which may contribute to better removal of pollution. For example, endophytes such as PDN can make plant hormones that tell the plants to make more roots. The roots start growing quickly and can be longer and denser than they are in trees without PDN . As a result, the PDN -containing plants can pull more nutrients out of the ground. PDN -containing poplar trees can also grow deeper and can possibly reach polluted regions that were previously unattainable.

MOVING FORWARD
This discovery has the potential to change the way we clean up environmental pollution. Endophyte-assisted phytoremediation is a whole lot cheaper than the usual practices, it is very e ective, and it is good for the environment. Likewise, it benefits wildlife as well as humans. But, because the discovery of endophyte-assisted phytoremediation is so new, the world still primarily uses the usual methods. The health of our planet depends on how we treat it, and it is our responsibility to clean up the mistakes of past generations. We must determine the future of our world by making the right decisions about how we manage our environment. By using the microorganisms