[Source: Mari N. Jensen, University of Arizona Communications] — Kathryn Plichta will be telling members of Congress about her research on Wednesday, April 25, 2007. She is one of about 80 undergraduates chosen by the Council on Undergraduate Research to participate in “Posters on the Hill.” Plichta is the only student from Arizona chosen to attend. The students will travel to Washington, D.C., to share their excitement about science with legislators and visit offices of their elected representatives. “I’m really excited about going,” said Plichta, a junior at The University of Arizona in Tucson. “It’s a great opportunity to give something back by encouraging funding for undergraduate research. I had the opportunity to do it, and I think other students should also.”
She studies Steinernema nematodes, tiny roundworms that live in the soil. Bacteria that live within this type of nematode kill insects. Her work is the first to closely examine the structure that houses bacteria within nematodes. Ultimately, research on the worm-bacteria symbiosis may lead to new non-chemical ways to kill insect pests.
Plichta is majoring in environmental science and science education at the UA and expects to teach science in middle school or high school after she graduates. A 2004 graduate of Sinagua High School in Flagstaff, Ariz., Plichta plans to visit Rep. Rick Renzi’s office during her day on the Hill. Her research advisor, S. Patricia Stock, a UA assistant professor in entomology, will accompany Plichta to Washington, D.C.
Plichta conducted her research Stock’s lab as a member of UA’s Undergraduate Biology Research Program, which receives funding from the Howard Hughes Medical Institute. The National Science Foundation also funded the research. Nematodes that parasitize insects, although small, are visible to the naked eye. They range in length from about 400 microns to 2000 microns — four to 20 times the width of a human hair. At a particular stage in their lifecycle, the nematodes crawl into an insect. The symbiotic bacteria then leave the nematode and kill the insect by turning the insect’s flesh into a nutritious soup for the nematodes. The juvenile nematodes mature and reproduce, and the next generation of juvenile nematodes crawls away to start the cycle again. Such nematodes use the larvae of insects that live in or on the soil, such as caterpillars, grubs and crickets. Although nematodes are already used for biological control of pests, little is known about what triggers the bacteria to leave the nematode and kill the insect. Within a nematode, the bacteria live in a pouch-like structure known as a vesicle. Stock suspects that there is some kind of chemical communication between the nematodes and the bacteria. “How do the bacteria know that they are inside an insect and it’s time to come out?” she said.
Stock said the vesicle is key to nematode-bacteria communication. She asked Plichta to catalogue the size and shape of the vesicles in various species of Steinernema nematodes. Plichta expected that differences between the vesicles would reflect the family relationships between the nematode species. That’s not what she found. Vesicles varied in size and especially shape, but didn’t seem to follow any patterns of family relationships between or have anything to do with nematode size. “Some were shaped like tadpoles, some like fish, some oblong and some like peanuts,” Plichta said.
Nematodes are see-through under a microscope. To measure their internal structure, Plichta put nematodes on a slide and examined them with a microscope that was hooked up to a camera and a computer. Using interference contrast microscopy and a computerized digital image system, she identified vesicles and measured them. Based on Plichta’s fundamental work on vesicles, new research in the lab is developing a better understanding of the nematode-bacterial relationship. Such understandings will help choose the best nematodes for biological control, Plichta and Stock said. For example, Plichta found very small vesicles in some nematodes. Those nematodes might not carry enough bacteria to be good biological control agents, the scientists said. Getting the chance to do research is a great educational experience, Plichta said. “Going through a formal process of scientific inquiry will help me teach students.”