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Measuring microbes

Variation in the abundance and activity of antibiotic bacteria in tropical forest soils may play a role in biodiversity.

Antibiotic-producing bacteria in soil are the source of many antibiotics used to combat diseases in humans and plants. But, surprisingly little is known about how these microbes impact tropical plant communities and ecosystems, where plant diversity, competition, and pathogen pressures are high.

A study published October 28 in the journal Biotropica represents a step toward a better understanding of the role antibiotic-bacteria play in the ecology of tropical forests. University of Minnesota researchers, led by Kristen Becklund, found that antibiotic production by soil bacteria was widespread, but that the abundance and activity of the microbes varied across the landscape depending, in part, on nutrient availability.

“Our results suggest substantial differences in the capacities of microbial communities to suppress soil-borne diseases in tropical forests,” says Becklund. “The fact that we are seeing all this variation is exciting because it means that these bacteria may be influencing diversity in tropical forests.”

Differences in the capacities of microbial communities to suppress soil-borne diseases in tropical forests could impact the composition of the forest itself. Antibiotics in soil are believed to act as weapons that allow microbes to kill their competitors, including pathogens. This antibiotic inhibition can lead to declines in populations of plant pathogens and can even result in the development of disease-suppressive soils. Because different plants are susceptible to different pathogens and diseases, variation in the abundance, effectiveness and specificity of microbially-produced antibiotics has the potential to influence not only plant disease and productivity, but also the composition of tree species in the forest.

“This study is an initial first step to open the black box of microbial community function in tropical forest soils,” says Powers.

Future studies will focus on the causes of the variation in density and activity and the potential consequences for tropical forest communities.

Becklund is a graduate student in the College of Biological Sciences’ Ecology, Evolution and Behavior program. Co-authors include Linda Kinkel, a professor in the Department of Plant Pathology in the College of Food, Agricultural and Natural Resource Sciences, and Jennifer Powers, a professor in the Departments of Ecology, Evolution and Behavior and Plant Biology in the College of Biological Sciences.

— Stephanie Xenos

Strep diversity and inhibition zones

Streptomyces are diverse soil bacteria known for their prolific production of antibiotics. Antibiotics can inhibit the growth of diverse plant pathogens in soil. Each clear area is the “kill zone” of an antibiotic-producing Streptomyces colony (which can be seen in the center) against the specified pathogen target, which has been spread over the surface of the growth medium. Photo credits: Nuttapon Pombubpa and Kinkel Research Group.

Kristen in the field with seedlings

Becklund in the field.

The Guanacaste region of Costa Rica where soil samples were collected.

Biotropica: November 2014 Editor's Choice