Tag: Microbes

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Field Focus: Our Microbial Menagerie

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Trillions of microorganisms inhabit us—inside and out. Scientists are surveying these microbial metropolises to learn more about their role in health. Microbiologists Darren Sledjeski of NIGMS and Andrew Goodman Exit icon of Yale University share a few details of what researchers have learned so far.

Vitruvian man filled with bacteria.
Researchers are surveying the microbes that inhabit us to learn more about their role in health. Credit: Andrew Goodman, Yale University.
  1. The majority of the microbes that inhabit us are bacteria. The rest of the microbial menagerie is fungi and viruses, including ones that infect the bacteria! Collectively, our resident microorganisms are referred to as the human microbiota, and their genomes are called the human microbiome.
  2. Our bodies harbor more bacterial cells than human ones. Even so, the microbiota accounts for less than 3 percent of a person’s body mass. That’s because our cells are up to 10,000 times bigger in volume than bacterial cells.
  3. Your collection of bacteria has more genes than you do. Scientists estimate that the genomes of gut bacteria contain 100-fold or more genes than our own genomes. For this reason, the human microbiome is sometimes called our second genome.
  4. Most of our microbes are harmless, and some are helpful. For example, harmless microbes on the skin keep infectious microbes from occupying that space. Microbes in the colon break down lactose and other complex carbohydrates that our bodies can’t naturally digest.
  5. Different microbes occupy different parts of the body. Some skin bacteria prefer the oily nooks near the nose, while others like the dry terrain of the forearm. Bacteria don’t all fare well in the same environment and have adapted to live in certain niches. The NIGMS Findings Magazine article Body Bacteria: Exploring the Skin’s Microbial Metropolis shows what types of bacteria colonize where.
Screenshot from the iBiology video.
Are we more microbial than human? Richard Losick, a microbiologist at Harvard University, explores that question in this video lecture produced by iBiology Exit icon.
  1. Each person’s microbiota is unique. The demographics of microbiota differ among individuals. Diet is one reason. Also, while a type of microbe might be part of one person’s normal microbial flora, it might not be part of another’s, and could potentially make that person sick.
  2. Host-microbial interactions are universal. Microbial communities may vary from person to person, but everyone’s got them, including other creatures. For this reason, researchers can use model organisms to tease apart the complexities of host-microbial interactions and develop broad principles for understanding them. The mouse is the most widely used animal model for microbiome studies.
  3. The role of microbiota in our health isn’t entirely clear. While it’s now well accepted that the microbial communities that inhabit us are actively involved in a range of conditions—from asthma to obesity—research studies have not yet pinpointed why or how. In other words, the results may suggest that the presence of a bacterial community is associated with a disease, but they don’t show cause and effect.
  4. Most of our microbes have not been grown in the lab. Microbes require a certain mix of nutrients and other microbes to survive, making it challenging to replicate their natural environments in a petri dish. New culturing techniques are enabling scientists to study previously uncultivated microbes.
  5. The impact of probiotic and prebiotic products isn’t clear. Fundamental knowledge gaps remain regarding how these products may work and what effects they might have on host-microbial interactions. A new NIH effort to stimulate research in this area is under way.
  6. There’s even more we don’t know! Additional areas of research include studying the functions of microbial genes and the effects of gut microbes on medicines. The more we learn from these and other studies, the more we’ll understand how our normal microbiota interacts with us and how to apply that knowledge to promote our health.
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Say Cheese

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Assorted cheeses
A biofilm of bacteria and fungi, commonly known as a rind, forms on the surface of traditionally aged cheeses. Credit: Elia Ben-Ari.

Biofilms—multispecies communities of microbes that live in and on us, and in the environment—are important for human health and the function of ecosystems. But studying these microbial metropolises can be challenging because many of the environments where they’re found are hard to replicate in the lab.

Enter cheese rinds. These biofilms of bacteria and fungi form on the surface of traditionally aged cheeses, and could serve as a system for understanding how microbial communities form and function. By sequencing DNA from the rinds of 137 artisan cheese varieties collected in 10 countries, Rachel Dutton and her colleagues at Harvard University identified three general types of microbial communities that live on their tasty study subjects. After individually culturing representatives of all the species found in the rind communities the scientists added them to a growth medium that included cheese curd. This approach allowed them to recreate the communities in the lab and use them to detect numerous bacterial-fungal interactions and patterns of community composition over time.

The scientists plan to use their lab-grown cheese rinds to study whether and how various microbes compete or cooperate as they form communities, as well as what molecules and mechanisms are involved. In addition to answering fundamental questions about microbial ecology, this cheesy research might ultimately yield insights that help fight infection-causing biofilms or lead to the discovery of new antibiotics.

Learn more:
Harvard University News Release Exit icon
Dutton Lab

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Restoring the Function of an Immune Receptor Involved in Crohn’s Disease

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Gut bacteria
Receptor proteins bind to bacterial cell wall fragments, initiating an immune response to remove bad gut bacteria. Credit: S. Melanie Lee, Caltech; Zbigniew Mikulski and Klaus Ley, La Jolla Institute for Allergy and Immunology.

Our bodies depend on a set of immune receptors to remove harmful bacteria and control the growth of helpful bacteria in our guts. Genetic changes that alter the function of the receptors can have an adverse effect and result in chronic inflammatory diseases like Crohn’s disease. Catherine Leimkuhler Grimes and Vishnu Mohanan of the University of Delaware researched a Crohn’s-associated immune receptor, NOD2, to figure out how it can lose the ability to respond properly to bacteria. In the process, they identified the involvement of a protective protein called HSP70. Increasing HSP70 levels in kidney, colon and white blood cells appeared to restore NOD2 function. This work represents a first step toward developing drugs to treat Crohn’s disease.

This work was funded in part by an Institutional Development Award (IDeA) Network of Biomedical Research Excellence (INBRE) grant.

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Meet Elizabeth Grice

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Elizabeth Grice
Elizabeth Grice
First job: Detasseling corn
Favorite food: Chocolate
Pets: An adopted shelter cat, Dolce
Favorite city: Athens, Greece
Hidden talent: Baking creative desserts
Credit: Bill Branson, NIH

Imagine a landscape with peaks and valleys, folds and niches, cool, dry zones and hot, wet ones. Every inch is swarming with diverse communities, but there are no cities, no buildings, no fields and no forests.

You’ve probably thought little about the inhabitants, but you see their environment every day. It’s your largest organ—your skin.

Elizabeth Grice, an assistant professor at the University of Pennsylvania, studies the skin microbiome to learn how and why bacteria colonize particular places on the body. Already, she’s found that the bacterial communities on healthy skin are different from those on diseased skin.

She hopes her work will point to ways of treating certain skin diseases, especially chronic wounds. “I like to think that I am making discoveries that will impact the way medicine is practiced,” she says.

Grice’s Findings

To investigate what role bacteria play in diabetic wounds, Grice and her colleagues took skin swabs from both diabetic and healthy mice, and then compared the two. They found that diabetic mice had about 40 times more bacteria on their skin, but it was concentrated into few species. A more diverse array of bacteria colonized the skin of healthy mice.

The researchers then gave each mouse a small wound and spent 28 days swabbing the sites to collect bacteria and observing how the skin healed. They found that wounds on diabetic mice started to increase in size at the same time as wounds on healthy mice began to heal. In about 2 weeks, most healthy mice looked as good as new. But most of the wounds on diabetic mice had barely healed even after a month.

Interestingly, bacterial communities in the wounds became more diverse in both groups of mice as they healed—although the wounds on diabetic mice still had less diversity than the ones on healthy mice.

“Bacterial diversity is probably a good thing, especially in wounds,” says Grice. “Often, potentially infectious bacteria are found on normal skin and are kept in check by the diversity of bacteria surrounding them.”

Grice and her colleagues also found distinctly different patterns of gene activity between the two groups of mice. As a result, the diabetic mice put out a longer-lasting immune response, including inflamed skin. Scientists believe prolonged inflammation might slow the healing process.

Grice’s team suspects that one of the main types of bacteria found on diabetic wounds, Staphylococcus, makes one of the inflammation-causing genes more active.

Now that they know more about the bacteria that thrive on diabetic wounds, Grice and her colleagues are a step closer to looking at whether they could reorganize these colonies to help the wounds heal.

Content adapted from the NIGMS Findings magazine article Body Bacteria.

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Learning More About Our Partners in Digestion

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Bacteroides ovatus
Bacteroides ovatus. Credit: Eric Martens, University of Michigan Medical School.

After eating, we don’t do all the work of digestion on our own. Trillions of gut bacteria help us break food down into the simple building blocks our cells need to function. New research from an international team co-led by Eric Martens of the University of Michigan Medical School has uncovered how a strain of beneficial gut bacteria, Bacteroides ovatus, digests complex carbohydrates called xyloglucans that are found in fruits and vegetables. The researchers traced the microorganism’s digestive ability to a single piece of the genome. They also examined a publicly available set of genomic data, which included information from both humans and their resident bacteria, and found that more than 90 percent of 250 adults harbored at least one Bacteroides strain with xyloglucan-digesting capabilities. These results underscore the importance of the bacteria to human health and nutrition.

This work also was funded by the National Institute of Diabetes and Digestive and Kidney Diseases.

Learn more:
University of Michigan News Release
University of Michigan Host Microbiome Initiative
Gut Reactions and Other Findings About Our Resident Microbes from Inside Life Science
Body Bacteria from Findings Magazine

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Gut Microbes Can Inactivate Cardiac Drugs

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Digoxin bacteria. Credit: CDC.

Bacteria in the gut can inactivate some of the medicines we take. Credit: CDC.

Doctors have known that a medication often prescribed to treat heart failure is inactivated by gut microbes, particularly a bacterial species called E. lenta. Now scientists have a better understanding of why. A Harvard University research team led by Peter Turnbaugh found that the heart drug digoxin turns on two E. lenta genes that help convert the drug into its inactive form, thereby making the medicine less effective. By measuring gene abundance, the scientists could reliably predict whether a microbial community could break down the drug. The researchers also identified a possible way to stop the process: add protein. Their studies using mice showed that a diet high in protein—and the amino acid, arginine, that helps E. lenta grow—increased digoxin absorption. These initial findings suggest that one day it may be possible to tailor digoxin therapy through diet modifications.

Learn more:
Harvard University News Release Exit icon
Turnbaugh lab Exit icon