‘Genetic Arms Race’ between Bacteria, Viruses Subject of Stimulus Grant

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Jay Lennon (view larger image)

The oceans teem with microscopic bacteria that produce much of Earth’s oxygen as they absorb carbon dioxide. Fast-mutating viruses also populate the seas, attacking marine bacteria in an ages-old evolutionary arms race.

An MAES researcher will probe that ancient dynamic against the backdrop of environmental and climate change and the pivotal role played by aquatic bacteria in maintaining the Earth’s biological balance.

“Even though viruses are important for regulating these bacteria populations, we find that a lot of rapid evolution occurs,” said Jay Lennon, MAES microbiology and molecular genetics researcher. In laboratory settings, the organisms known as cyanobacteria can take just weeks to evolve resistance to viruses, Lennon said, and viruses similarly mutate to find new ways to infect them.

Cyanobacteria play a vital role in sequestering ocean nitrogen and phosphorus. At the same time, they remove carbon dioxide from the air and produce oxygen. Understanding how they evolve to resist viruses could unlock information critical to environmental and climate studies, Lennon said.

Lennon will pursue his research using a $199,000 National Science Foundation grant, which includes American Recovery and Reinvestment Act funds. He will work with microbiologist Steven Wilhelm of the University of Tennessee and biochemist Nathan VerBerkmoes of Oak Ridge National Laboratory, both funded by other grants.

One of the most common mechanisms for virus resistance is evolutionary change or loss of cell surface receptor molecules—the structures through which viruses enter their hosts. The researchers will study such changes in natural cyanobacteria populations. Once key receptors are identified, Lennon will focus on generation of virus-resistant bacterial cell lines and species competition experiments at his lab at the W.K. Kellogg Biological Station.

Marine viruses have been subjects of interest only since the late 1980s, Lennon explained, and little about how that parasite-host relationship operates is understood. Just a milliliter of seawater can contain up to 10 million viruses, he said, some of which are deadly to some cyanobacterial hosts but not to others. The viruses also could wield substantial influence on global environmental cycles by killing vulnerable cyanobacteria and changing the nature of marine bacterial populations through natural selection, the researchers said.

Earlier research by MAES evolutionary biologist Richard Lenski and others has shown that virus-based natural selection can negatively affect cellular organisms’ ability to take in nutrients—that there’s a fitness trade-off in bacterial evolution.

Cyanobacteria are sometimes referred to as blue-green algae but are in fact bacteria more closely related to organisms such as E. coli than to green algae. Ancient forms of life found on fossils billions of years old, cyanobacteria might be responsible for formation of many of today’s oil and iron ore deposits, and they remain one of the most prevalent forms of bacteria on earth.

Cyanobacteria population explosions in some freshwater lakes in recent hot seasons have released toxins that killed waterfowl and forced closure to recreation. Such blooms are not typical in oceans.

In addition to the NSF grant, Lennon’s work is supported by the Michigan Agricultural Experiment Station, the Gordon and Betty Moore Foundation, the Broad Institute at Harvard University and the Massachusetts Institute of Technology, which will sequence virus genomes for the research project to genetically evaluate how they evolved.

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