New Test To Find, Recruit Pest-Fighting Bacteria

ARS nematologist Greg Noel and colleagues developed the method to help resolve confusion surrounding Pasteuria's taxonomic classification and clarify its parasite-host relationship with soil-dwelling roundworms like the soybean cyst nematode, a crop pest that costs $324 million to $1.4 billion annually in U.S. soy losses.

Since Pasteuria can't be cultured in the lab, researchers seeking to determine its genetic affiliation must resort to extracting DNA from the spore-infected bodies of nematodes. It's a laborious, time-consuming affair that's sometimes prone to DNA contamination by other microbes, according to Noel. He is in the ARS Soybean/Maize Germplasm, Pathology and Genetics Research Unit at Urbana, Ill.

There, rather than using centrifuging, heat and chemicals to obtain Pasteuria DNA, Noel resorted to "glass bead beating." The procedure involves grinding spore-infected nematodes so that any DNA within them is released into a sterile solution. Lab-built molecules called primers are then added. These bind only with Pasteuria DNA--if it's present--and ready the material for amplification by polymerase chain reaction. The DNA can then be cloned and sequenced as Pasteuria's unique, genetic fingerprint.

According to Noel, the method is fast, easy to use, and highly specific. Besides its taxonomic applications, it should aid scientists in identification of Pasteuria species that attack different nematode species. Some of these Pasteuria also complete their life cycles in juvenile nematodes, while others do so in female nematodes.

Either way, the pests face a grisly demise. Within a month, for example, infected soybean cyst nematode females become fragile to the point of crumbling apart, a fate that diminished the pest's population by 87 percent in Noel's field studies at Urbana.