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Research Roundup

07 December 2006

A new target for anti-anthrax drugs

Berkeley chemists have discovered a trick that anthrax bacteria use to make an end run around the body's defenses, but that may turn out to be their Achilles' heel. They were part of a team that uncovered the trick while studying how these deadly bacteria steal iron from their human hosts to grow and reproduce.

Anthrax bacteria are known to produce two small molecules - bacillibactin and petrobactin - that snatch iron away from the human body's iron-transporter molecules, called transferrin. These scavengers, or "siderophores," are essential to anthrax's ability to grow rapidly, especially after the spores are inhaled, though why the bacteria need two siderophores to do the job has been an enigma.

The new study shows why anthrax bacteria require two siderophores working by two different mechanisms. Siderocalin, the human immune protein, binds bacillibactin and effectively sidelines it, the researchers found. Apparently, anthrax fields a second "stealth" iron scavenger, petrobactin, to get around the human defense against the first scavenger. Petrobactin is not bound by siderocalin.

As far as is known, the human immune system has yet to launch a successful counterattack against the stealth siderophore, but that doesn't mean humans can't design one of their own, says Ken Raymond, professor of chemistry and a faculty scientist at Lawrence Berkeley National Laboratory. His team is working with colleagues from the Fred Hutchinson Cancer Research Center in Seattle to explore how their discovery could be used to diagnose or treat anthrax.

- Robert Sanders

Reducing air pollution could increase rice harvests in India

New research conducted by scientists at Berkeley and UC San Diego indicates that reductions of human-generated air pollution could create unexpected agricultural benefits in one of the world's poorest regions.

Following a dramatic increase in rice harvests in India during the "Green Revolution" of the 1960s and 1970s, harvest growth has slowed since the mid-1980s, raising concerns about food shortages. No explanation yet proposed has taken into account the complex interactions of two pollution-related sources of climate change: atmospheric brown clouds (ABCs), which form from soot and other fine particles in the air (collectively termed aerosols), and the better-known problem of global warming caused by greenhouse gases such as carbon dioxide.

UC researchers analyzed historical data on Indian rice harvests and examined the combined effects of atmospheric brown clouds and greenhouse gases on growing conditions. They found that those effects were negative and were greater after the mid-1980s than before, coinciding with the observed slowdown in harvest growth. They estimate that harvests would have been 20 to 25 percent higher during some years in the 1990s if the negative climate impacts had not occurred.

Previous research had found that brown clouds have made the Indian subcontinent drier and cooler. Although this suggests a climatic tradeoff whereby reductions in aerosols potentially unleash a stronger warming trend, the current study indicates that joint reductions in the two types of pollutants would, in fact, benefit Indian rice farmers. This is because reductions in aerosols would enhance rainfall, while reductions in greenhouse gases would reduce the higher nighttime temperatures that can negatively affect the growth of the rice plant.

Maximilian Auffhammer, assistant professor of agricultural and resource economics, said that "while this study focuses on India's rain-fed states, ABCs exist throughout Asia's main rice-producing countries, many of which have experienced decreasing growth rates in harvests, too. Furthering our understanding of how air pollution affects agricultural output is very important to ensure food security in the world's most populous region."

- Sarah Yang