Archive for February, 2012
The common cottontail rabbit — ubiquitous in forests, suburban woods and backyard gardens — seems an unlikely agent of bioterrorism. However, Jason Huntley in the Medical Microbiology and Immunology Department has rabbits on his radar; they’re the best-known reservoirs of the deadly pathogen and potential bio-weapon he‘s studying.
Francisella tularensis is a bacterium high on the U.S. government’s list of Category A Select Agents, a rogue’s gallery of molecular bad guys that also includes anthrax, botulism and plague. Capable of surviving in species that range from an amoeba in a freshwater stream to flies, ticks, mammals and humans, F. tularensis is the cause of tularemia, which can kill an adult in as little as five days.
Particularly worrisome, Huntley says, is how easily F. tularensis can be aerosolized. (Documented cases include those caused by inhaling the aftermath of sick or dead rabbits caught in lawn mowers.) “The bacteria could easily be dispersed by a small device,” he notes. “And all it takes is one Francisella bacterium to kill a human, whereas for anthrax it’s about ten thousand spores.”
Huntley and his group study aspects of proteins that exist on the bacteria’s surface. One such characteristic of these proteins is their role in virulence: How can F. tularensis cause life-threatening disease so quickly? “We now have evidence that these proteins are involved not only in the basic survival functions of the bacterium, but also in attaching to host cells, invading them and killing them,” he says.
“We also study the bacteria from a defensive standpoint, for vaccine development. Because Francisella kills so quickly, the body doesn’t have time to react, to create the antibodies and recruit immune cells necessary to kill the invader. Developing a vaccine would allow the human body to have those defense mechanisms already in place.”
Studying such deadly pathogens has profound implications for other diseases, he adds. “If you can understand how they cause disease, you can start to ask questions about how many other bacteria and viruses work: pneumonia, GI infections, skin infections. The list goes on and on.”
Funded by the National Institutes of Health, Huntley’s work is under consideration by the U.S. Department of Defense.
Plants, insects and fungi in every sort of ecosystem have over time developed complex, mutually beneficial interactions that allow delicate coexistence. The pesticide/herbicide/chemical fertilizer revolution, however, has overridden these ecological relationships.
Natural may be best, however, according to Dr. Stacy Philpott, UT assistant professor of environmental sciences, who’s been researching an organic coffee farm in Mexico. There, an intricate dance of interdependence exists between an unlikely set of partners: a feisty ant species (Azteca instabilis); the green coffee scale insect; and the predatory lady beetle. All three — plus some potential players waiting for a cue — play critical roles in bringing the coffee crop successfully to market.
The ants and scales form a symbiotic relationship in which the ants protect the scales from predators and parasites. In return, the scales secrete a sweet honeydew that’s eagerly taken by the ants. It’s made more complex by a predatory lady beetle: Both adults and larvae feed on coffee scales. Azteca ants can protect scales by fending off adult beetles, but can’t make a dent in the larvae.
The ants’ success at repelling another scale enemy, a parasitic wasp, inadvertently chases away other wasps that attack beetle larvae, adding to the system’s complexity. The ants have their own enemy, too: a parasitic fly that can limit their presence in the ecosystem. Likewise, the lady beetles can make an impact on ant numbers by preying on the scale and limiting the available honeydew.
Perfect balance is achieved when the ants are limited by beetles and parasitic flies. Both ants and beetles thrive, the latter keeping the crop-damaging scale insects under control.
But wait — scale insects can also be attacked by the white halo fungus. That same fungus, though, is an enemy of coffee rust, a disease that in the past wiped out entire coffee-growing regions. The rust exists in Central and South America; white halo fungus is a powerful rust eradicator only in places where it’s already mounting a major attack on scales — places most likely to be where the indefatigable Azteca ants are protecting their honeydew-producing scales.
The complexity of the relationships on the successful coffee farm in southern Mexico wouldn’t have become clear without close research, Philpott says. “Studying these interactions is important for understanding how ecosystems work, especially how agricultural systems work,” she adds. “Industrial agriculture is largely aimed at the target pests — controlling an insect or fungal disease by applying something. It wreaks havoc on biodiversity, and causes loss of habitat, contamination and related health problems.
“One solution to these problems is looking at this extremely complicated agricultural system that has so many interlinking components and asking how we can achieve natural forms of disease- and pest-control using complex food webs.”
Fish feces seem an unlikely tool to help preserve the world’s much-stressed coral reefs. John W. Turner Jr. in the Department of Physiology and Pharmacology knows better; he and his team of researchers have been using fecal material from parrotfish in the Virgin Islands to link their stress with that of the reefs.
The project, funded in large part by conservation groups, centers on cortisol, a hormone produced by the adrenal gland in response to stress. The hormone serves as an excellent biomarker and stress monitor for both mammals and fish, and is detectable in their waste matter.
For a fish, stress goes beyond the presence of hungry predators. Nitrite — present in water due to fertilizer runoff — creates the condition as well, eventually impacting their numbers. That in turn affects the reefs. “One of the biggest threats facing coral reefs today is that we’re seeing much lower diversity in fish populations, lower reproductive success and slower growth rates in those who do reproduce” says Turner. “The bottom line is fewer fish.”
It‘s a fraught line because fish play a critical role in reef ecology. Take parrotfish: Grazing on the coral’s surface, the colorful fish eat away algae that unchecked would block sunlight from the coral and prevent vital photosynthesis.
“Parrotfish are part of most coral reef systems worldwide, so if you can find a reliable biomarker for the parrotfish family, you can apply it to almost any coral reef system,” Turner explains.
Cortisol was the first stress biomarker the researchers identified by analyzing parrotfish fecal matter. Taking a further step, they began looking at gene expression associated with stress response, and with the fish’s reproductive success. “We’d like now to know what genes are being turned on and off by stress. If we know, we have a template to tell us what type of stressor is affecting that area,” Turner says.
Recently the team was able to isolate RNA from four specific genes. The discovery encouraged them to begin developing a hierarchical biomarker system to detect and isolate individual stressors in an environment.
That would create a powerful tool for everyone interested in conservation, Turner notes. “It’s to the advantage of resort builders, for example, to know what the conditions are before they begin to build near a pristine coral reef area, then what they are as they build, open and operate.
“The relationship between developers and biologists used to be antagonistic, but that’s counterproductive. Everybody, including the public, benefits from knowing about the environment before and after. It makes constant monitoring possible.”
Far from spurning fish poop’s Ew! factor, Turner is excited: “Coral reefs are in bad enough shape as it is, and we’d all like to stem their degradation. We think this is the path to do it.”