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Vol. LXV, No. 6
March 15, 2013

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Profound Effects on Human Health
Microbiologist Studies How Animals, Microbes Have Coevolved

Dr. Margaret McFall-Ngai

Dr. Margaret McFall-Ngai

We tend to think of germs as the enemy, but some microbes are allies essential to our existence.

Trillions of microorganisms live on and in our bodies. Recent research reveals that many of them contribute to vital life functions from circulation and digestion to immune defenses.

“We know that humans have, throughout their evolutionary history, been influenced by interactions with microorganisms,” said Dr. Margaret McFall-Ngai, professor of medicalmicrobiology and immunology at the University of Wisconsin. “Microorganisms seem to be impacting just about every aspect of our biology.” For instance, she said, the products of microbial activities are absorbed from the intestine into the circulatory system and affect every cell serviced by blood.

Speaking at a recent Wednesday Afternoon Lecture in Masur Auditorium, sponsored by the Foundation for Advanced Education in the Sciences, McFall-Ngai marveled at how technology is changing how we view the whole biosphere. She said an advance in molecular technology and DNA sequencing “is enabling and revolutionizing how we see the biological world.”

Introducing her, NIH director Dr. Francis Collins said, “She comes to us at a very interesting time because the amount of data that’s possible to generate on the microbiome has been expanding drastically in the past few years with the advent of technologies and the Human Microbiome Project.”

The NIH-sponsored project convened hundreds of scientists from dozens of research centers to examine hundreds of healthy human volunteers. Through DNA sequencing and genetic analysis, researchers identified and studied all of the microorganisms that habitually exist on and in our bodies.

Microbes have an impressive metabolic scope, said McFall-Ngai, who has spent decades studying host responses to interactions with beneficial microbes. A long-time expert on symbiosis, she and her collaborators have been analyzing the relationship between squid and bacteria.

The Squid and the Vibrio: A Codependence Success Story

The research examines the tiny bobtail squid (Euprymna scolopes) and its gram-negative bacterial partner Vibrio fischeri. This symbiotic relationship helps us understand how two different species form a persistent relationship and coexist to survive.

That bioluminescent glow you might see in the ocean at night is light emitted by living organisms. The bioluminescent vibrio living in this species of squid produces the glow from the animal’s light organ. Glowing helps the squid blend into its surroundings and eliminate its shadow against the moonlight to avoid detection by predators.

“Our idea of relationships in the biological world is drastically changing on a yearly basis,” said McFall-Ngai.

“Our idea of relationships in the biological world is drastically changing on a yearly basis,” said McFall-Ngai.

Symbiosis is a central tenet of animal biology. McFall-Ngai’s work examines how the symbiont population, the Vibrio fischeri, subsists over its host squid’s lifetime, so that the symbiont does not overgrow the host and the host does not eliminate it. This balancing act has prompted further investigation of the similarities and differences between pathogenic and beneficial animal-bacterial interactions.

Recent studies have demonstrated that beneficial and harmful microbes often use the same molecules to mediate their interactions on host-cell surfaces. McFall-Ngai gave one example of the high levels of toxic nitric oxide emitted by the squid, through which the vibrio must navigate to colonize their host.

The vibrio-squid model gives us insights into the larger world of microbial interactions with different species, how bacteria colonize humans and other animals and the role microbes play in our health.

“Our idea of relationships in the biological world is drastically changing on a yearly basis,” said McFall-Ngai. She cited the three domains that comprise the biological world—eukarya, archaea, bacteria—but said due to the impact of horizontal gene transfer, there may not be a tree of life as we know it; additional groups and kingdoms could be possible.

McFall-Ngai underscored the importance of technology in advancing biological discovery. While some institutions have a more conservative approach, she expressed her hope that universities and NIH will take a forward-thinking trajectory to the bio-tech revolution.

Microbiome Resources:

View the webcast:
McFall-Ngai’s lab web site:
Human Microbiome Project:

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