Darwin Chronicles

February 2006

Ants have weapon to fight parasites

Certain types of ants harbor antibiotic–producing bacteria on their body that protect their crops of fungus from parasitic invaders.

Writing in the journal Science, an international team led by University of Wisconsin–Madison bacteriologist Cameron Currie, MSc, PhD, concluded that theants house the bacteria in specialized, highly adapted cavities, and nourish them with glandular secretions, an indication that the ants, bacteria, fungus and parasites have likely been evolving together for millions of years (2006;311:81-83).

“Every ant species [that we have examined] has different, highly modified structures to support different types of bacteria,” Currie said in a prepared statement. “This indicates the ants have rapidly adapted to maintain the bacteria. It also indicates that the coevolution between the bacteria and the ants, as well as the fungus and parasites, has been occurring since very early on, apparently for tens of millions of years.”

The fact that the species have coexisted for so long means there might be a mechanism in place to decrease the rate of antibiotic resistance, which could help address a significant problem facing modern medicine, Currie added.

“We can learn a lot about our own use of antibiotics from this system,” he said.

Currie studies the intricate relationships between certain species of ants in Central and South America. Although the ants and their fungus gardens had been closely studied for dozens of years, Currie was the first to identify the role of bacteria and the antibiotics they produce. He noted that certain white spots on the ants, which were previously dismissed as “waxy blooms,” were actually colonies of bacteria.

In the latest phase of his research, Currie, who began this study when he was at the University of Kansas, and his team removed the external blooms of bacteria from two ant species in the genus Cyphomyrmex and examined the exoskeleton beneath with a high-powered microscope. Their investigation revealed crypts attached to endocrine glands.

In fact, the crypts are specially adapted to the type of bacteria each species harbors – evidence, he said, that the ants are capable of rapidly changing to maintain their bacterial residents.

The degree of specialization indicates that the association between the ants and the bacteria is ancient, Currie said, and likely vital to the species’ survival. The phenomenon extends beyond the two species of Cyphomyrmex ants in the study to about 210 species of fungus–growing ants.

“For me, it shows us how little we know about natural systems and microbes in nature. Fungus-growing ants are very well studied, yet this morphological characteristic went unnoticed until now. What other organisms might be taking advantage of this type of association? What don’t we know about other systems that are not as closely studied as these ants?,” Currie asked.

The National Science Foundation, the K.U. Leuven Research Fund and the state of Wisconsin supported the project.

All but eight states now in national disease reporting system

All but eight states are now actively participating in the National Animal Health Reporting System (NAHRS), according to a report presented at a meeting of the Committee on Animal Health Information Systems, held in Hershey, Pa.

The 42 participating states represent 86% of the cattle, 66% of the swine, 90% of the sheep, 67% of the poultry and 84% of the catfish value of U.S. production for these commodities.

Under the NAHRS, state animal health officials report monthly on the occurrence of specific diseases listed by the World Organization for Animal Health (OIE). The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service uses this information for the annual report that the United States makes to the OIE.

The report indicated an increasing number of states are reporting their disease and health information through an online reporting system. Twenty-eight of the 42 states in the system are using this method of reporting.

Under a pilot project in California designed to improve data quality, hardware and software has been developed so that field inspectors can record information during a farm visit, which is automatically routed to a number of different place that have a need for it, such as diagnostic laboratories and state and federal regulatory offices.

The system also allows for test results from diagnostic laboratories to come back to the inspector – who can pass this information on to the farmer – and state and federal regulatory offices.

The committee is a joint effort of the U.S. Animal Health Association and the American Association of Veterinary Laboratory Diagnosticians.

Canine cancer vaccine shows early promise

After promising results from work done in collaboration with cancer specialists from Arizona, California and Michigan, the University of Wisconsin–Madison School of Veterinary Medicine has hired a full–time technician to produce its experimental anti-cancer vaccine for dogs.

“Not all dogs with melanoma respond to this treatment,” Ilene Kurzman, MS, EdD, researcher in the veterinary medical school’s oncology section, said in a statement. “But those that do seem to do quite well.”

Melanoma, the equivalent of one form of skin cancer in humans, is very aggressive in dogs. It usually manifests itself in or around the mouth or toes. Despite conventional treatment, 75% of dogs with oral melanoma die within one year.

About 40% of dogs with a melanoma tumor, however, responded to the experimental vaccine, which researchers created from actual melanoma tumor cells. In about 12.5% of the treated dogs, the tumor completely disappeared.

According to Kurzman, the vaccine was created from dog melanoma cells grown in the laboratory. Researchers treated the cells so they can no longer divide and cause a tumor. Then, they inserted DNA, which directs the cells to secrete an immune stimulant, into these cells. This combination of cells and immune stimulant, when administered as an injection into a patient’s skin, has been shown to stimulate the immune system to specifically fight against melanoma cells.

Dogs that first had surgery for their melanoma and then received vaccine lived cancer–free about twice as long as dogs in previous studies that did not receive the vaccine, researchers said. Further research is needed to improve the vaccine so that a higher percentage of dogs with melanoma will respond, researchers said.

Bacteria more diverse in Arctic tundra than forest soil

The soil beneath the arctic tundra is home to a greater diversity of microorganisms than nearby boreal forests, according to researchers from British Columbia.

Boreal forests (cold temperature forests found in the northern hemisphere) and arctic tundra cover 22% of the earth’s terrestrial surface. These environments are sensitive to climate change, and variation in their productivity can substantially affect the global climate, according to a report in the journal Applied and Environmental Microbiology (2005;71:5710-5718).

Researchers took soil samples from three arctic tundra sites and three boreal forest locations, and analyzed for bacterial diversity. They found a broader range of microbial presence in undisturbed arctic tundra soil with the highest diversity identified in a sample from an extreme northern location.

“This report demonstrates that the Arctic serves as an unrecognized reservoir of microbial diversity and thus biochemical potential,” the researchers said in a release.