4:25 p.m., Sept. 16, 2008----A significant percentage of life in the ocean is made up of bacteria, also known as bacterioplankton, and a University of Delaware-led research team is working to learn more about which bacterioplankton are active and which remain inactive in various open ocean environments.

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The UD team is headed by principal investigator Barbara Campbell, assistant professor of marine and Earth studies, and co-principal investigator David Kirchman, the Maxwell P. and Mildred H. Harrington Professor of Marine Studies, who have been awarded a $445,000 National Science Foundation grant to conduct the research. They are working in collaboration with John Heidelberg, associate professor of biological sciences at the University of Southern California.

Typically, more than 1 million bacterioplankton cells can be found in each milliliter of seawater and they contribute greatly to important biogeochemical cycles in the ocean, including carbon, nitrogen and sulfur cycling.

However, Campbell said, there has been a longstanding debate as to the activity of all of these bacteria. For instance, there is a great amount of microbial diversity--some say more than 1,000 to 10,000 types in a milliliter of seawater--but only a fraction, less than 50 percent, seem to be actively taking up organic compounds.

Also, it is impossible to measure growth rates of individual bacterial types in the oceans using standard ecological techniques, she said.

“We believe that different bacteria are active under different environmental conditions,” Campbell said. “Therefore, given the large amount of bacterial diversity in the ocean, of which a significant percentage of the bacteria are rare, we hypothesize these rare bacteria are inactive and waiting until the environmental conditions are optimal for their growth and activity.”

The researchers said they hope to link the diversity and type of bacteria to the processes they are carrying out. For instance, Campbell said they would be studying the diversity and type of bacteria that are actively metabolizing complex carbohydrates and digesting proteins and whether this changes with the seasons. “By looking at the transcriptome of the community, the metatranscriptome, we can tell which genes are actively being transcribed in our samples,” she said.

The research team will be traveling to the Sargasso Sea, a large region in the middle of the North Atlantic Ocean, twice a year for two years to collect samples. The sample collection will be in collaboration with Michael Lomas of the Bermuda Institute of Ocean Sciences and a principal investigator with the Bermuda Atlantic Time-series Study.

Samples will be collected during the spring phytoplankton bloom when heterotrophic bacterial production is lowest and during the peak of bacterial production in summer.

“This project will do much to alter our perception of microbial processes in the ocean by providing answers to long-standing questions about activity and standing stocks of bacterial populations and by linking metabolic processes to the extensive environmental genomic data now becoming available,” Campbell said.

Campbell received her doctorate in microbiology from Cornell University, and her research interests center on the function and structure of microbial communities at the molecular level.

Kirchman received his bachelor's degree in biology from Lawrence University and his master's degree and doctorate in environmental engineering from Harvard University.

Article by Neil Thomas