Rhizobium
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If you think cleaning up your room is a
hassle, just imagine having to clean up a hazardous waste site! When it comes
to toxic chemicals that have escaped into the environment, clean-up duty can
become downright dangerous. |
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Maybe youve tried to bribe your little brother or sister
to clean up your messy room. Well, scientists are trying a similar trick. But
instead of a sibling, theyre bribing tiny plant bacteria into
tackling the dirty job of toxic clean-up. |
Their bacterial recruits belong to a family called
Rhizobium, which lives on alfalfa and
soybean roots. There, the helpful microbes supply the plants with nitrogen for
food and growth. This partnership also helps keep the soil fertile and healthy.
Thats something you generally wont find at contaminated site, like
a landfill or mining operation. |
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(Photo: The roots of
soybean and alfalfa plants help keep soils healthy and fertile, thanks to the
busy little Rhizobium bacteria that live in them.) |
To get the bacteria to clean soils polluted by chemicals,
scientists first had to give the microbes instructions. These included a
special gene that
tells the bacteria how to make and secrete an
enzyme from its cell walls. |
Think of this
enzyme as a kind of carpet cleaner your little brother or sister might use in
your room. But instead of dirt and grime, the bacterias enzyme helps
clean soils contaminated by toxic chemicals like TNT or toluene. Toluene is a
common ingredient in fuel and dyes. |
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(Photo: a cross-section of a root
nodule--a tiny lump in which Rhizobium bacteria would do their clean-up work.
Each nodule is occupied by about a billion of the rod-shaped microbes.)
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TNT, you probably know, is the
highly flammable stuff thats found in explosives like dynamite. Once
these explosives detonate, their basic chemical building blocks get left behind
in soils and sometimes the water. This is common problem at military sites, for
example. The chemicals also can escape into the environment from ammunition
plants. |
But in the lab,
scientists found that the bacterias enzymes break down these TNT building
blocks into harmless substances. |
TNT isnt
the only chemical the busy little bacteria will take on. The microbes also
break apart DNT. This is a chemical that makes plastic and Styrofoam such a
serious waste disposal problem. |
You put
them in landfills and they just sit there. They dont degrade
quickly, says Gail Hollowell, pictured at right. As a student not long ago, she
helped ARS and Howard University scientists study the Rhizobium
bacteria.
Her mentors,
ARS horticulturist David
Kuykendall and HU professor Sisir Dutta, came up with the idea of hiring on
the Rhizobium bacteria. Their partners include scientists Fawzy Hashem
and Bill Gillette, as well the U.S. Army Corps of Engineers.
The Corps is
looking for cheap methods of restoring the health of contaminated soils at
military sites. But it wants something that wont cause more environmental
harm. |
(Photo: Gail Hollowell, posing with her bacterial clean-up crew--contained in
test tube and on roots of potted alfalfa plants.) |
The scientists imagine coating the
bacteria onto alfalfa seeds, and then planting the seeds in polluted soils.
That could cut the cost of trucking the soils off to special
treatment plants. It could also mean less need for human clean-up crews, and
lower their risk of exposure to dangerous chemicals. |
Scientists
arent sure the bacteria and their plant partners will be the magic
bullet in the war on wastes. |
It would
be nice if this completely decontaminated the fields, says Hollowell, now
a National Institutes of Health researcher. But even if it doesnt,
and you only get partial degradation, thats still an
improvement. |
--By
Jan Suszkiw, Agricultural
Research Service, Information Staff
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