Marks the Spot
July 22, 2003
Rice is the latest ally of scientists
battling the Colorado potato beetle.
Scientists with the Agricultural Research
Service are using rice grains to determine if a newly discovered biocontrol
bacterium--now being tested to control the beetle--is in the soil. The beetle
feeds on potato, eggplant and tomato plants.
The purple bacterium, Chromobacterium suttsuga, kills beetles in
laboratory studies. But before applying the bacterium to the soil, scientists
need to know how long it survives, if it changes the soil or if it's harming
the environment or other beneficial organisms.
For these experiments, microbiologist Phyllis Martin and her colleagues in
the ARS Insect Biocontrol
Laboratory in Beltsville, Md., adapted a technique to detect C.
suttsuga in the soil. Martin found that by using sterile rice grains, she
could detect small amounts of the purple bacteria--fewer than 50 cells in about
a teaspoon of soil.
In the experiments, rice grains are placed on moist soil. In about three
days, some rice grains turn purple if C. suttsuga is present. The
percentage of purple-colored rice can then be used to determine the original
amount of bacteria in the soil. According to Martin, the test has proven to be
as sensitive as more expensive methods that depend on copying DNA, and it has
the advantage of simultaneously detecting, quantifying and determining that the
bacteria are alive. The rice method takes a little longer, but detection of
bacteria in soil is not as time-critical as detection of bacteria in humans.
This simple technique also works for other bacteria that are pigmented, such
as the red bacterium, Serratia marcescens. It also kills Colorado potato
beetle, but not as effectively as the purple bacterium does.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.