ISU Researcher Receives New Grant to Study Soil Bacteria

May 3rd, 2005

An Iowa State University researcher has been awarded a three-year, $435,000 National Science Foundation grant to study soil bacteria. Larry Halverson, a senior lecturer in Iowa State's Department of Plant Pathology, is studying how extracellular polysaccharides shape soil microbial communities.
Example of a biofilm developing on a surface. This image illustrates the coordination among cells that takes place during biofilm development.
Extracellular polysaccharide is the technical term used to describe the slimy coating that covers microbial communities. The slime usually is composed of large sugar molecules that have different water-absorbing properties, much like a sponge absorbs water.

"In soil or on plant leaves, bacteria develop this slimy coat to create a nice, and preferably wet, home that helps them survive," Halverson said. "This slime coat is like covering yourself in a wet towel on a hot, sunny day — it cools you off and keeps you from drying out like a raisin."

Halverson said soil bacteria become encased in slime in a structure called a biofilm. "My goal is to understand how bacteria build these biofilms when water is limited, how their structures differ under various conditions, and how bacteria change the slime layer to soak up more water when the soil becomes dry."

Halverson also is examining how different polysaccharides influence the way bacteria accumulate on a plant or soil surface to create a biofilm, and how life in a biofilm influences their ability to survive droughty conditions.

"This work is very fundamental, but it has the potential to allow us to better understand how pathogens survive winter or dry conditions or survive plant defenses," Halverson said. "It also will provide insight into how microbial communities can be manipulated to alter the soil environment to retain water longer during droughty conditions."

Halverson acknowledges that in many cases, bacteria survival isn't a good thing. "But sometimes their survival is beneficial. For instance, bacteria can eat organic pollutants," he said. "We'll use what we're learning to develop a model of the way things such as gasoline or livestock wastes break down in soil, and how changes in soil moisture influence those beneficial activities."


Larry Halverson, Plant Pathology, (515) 294-0495,
Susan Thompson, Communications Service, (515) 294-0705,