We and Our Microbes are In This Together
Next time your digestive system malfunctions in some embarrassing way, you can always blame man's best friend - not the dog, but the bacterial cells that live in your intestines. Not everyone has a dog but we all have enormous communities of bacteria that help us digest food. They don't always do a perfect job, but without them we'd have trouble surviving. In fact, our bodies have about ten times as many bacterial cells as human cells, said David Artis, a microbiologist at the University of Pennsylvania. "Some people have even joked that if one considers the meaning of life," he said, "it could boil down to us being vessels to carry around bacteria."
We and Our Microbes are In This Together
Here’s my weekly column, which will also run in Monday’s Health and Science section of the Philadelphia Inquirer
Image is from Penn and reportedly shows a color enhanced tissue section from a healthy mouse. The mouse cells are green and bacterial cells are purple.
Next time your digestive system malfunctions in some embarrassing way, you can always blame man’s best friend – not the dog, but the bacterial cells that live in your intestines. Not everyone has a dog but we all have enormous communities of bacteria that help us digest food. They don’t always do a perfect job, but without them we’d have trouble surviving.
In fact, our bodies have about ten times as many bacterial cells as human cells, said David Artis, a microbiologist at the University of Pennsylvania. “Some people have even joked that if one considers the meaning of life,” he said, “it could boil down to us being vessels to carry around bacteria.”
Artis has been studying our relationship to our resident microbes, the vast majority of which live in our intestines. Recently, he’s focused on how they know to be so friendly and refrain from spreading around the body and making us sick.
He’s found these so-called commensal bacteria aren’t friendly by nature. If that enormous load of intestinal bacterial cells got out into other parts of the body, “they could kill us,” he said. Luckily, our immune systems have evolved the ability to police these bugs, keeping them from spreading beyond the intestines, he said. It’s a constant process of negotiation between our cells and theirs. When that symbiotic harmony breaks down, good bacteria can escape and make us sick.
All animals carry around symbiotic bacteria, said Rob Knight, an evolutionary biologist at the University of Colorado, Boulder. Bacteria are good at living with other organisms, and our relationship with them probably predated the origin of the animal kingdom some 600 million years ago.
But now, we humans and our resident microbes are facing an unprecedented evolutionary situation, he said. First there was agriculture, which led to a radical change in the human diet, and then, more recently, the switch to an industrialized diet of refined foods. And in the 20th century we changed our internal ecology with antibiotics. Communities we’ve lived with for millennia are changing or breaking down, he said.
Several years ago, Knight was part of a study suggesting that delivering babies by caesarian section had the unintended consequence of changing their internal biota. In a small pilot study he and researchers from the University of Puerto Rico found that vaginally delivered babies were colonized mostly by bacteria they picked up from mom on the trip out, while c-section babies were full of staph that had come from the environment.
Knight said he anticipates the ability to learn much more about our microscopic friends thanks to a $160 million effort to sequence their DNA known as the human microbiome project. By cataloging the microbial ecosystems of about 250 individuals, he said, scientists will be able to figure out what constitutes a normal mix of bacteria types and how our bacteria might signal disease.
Penn’s Artis said there are a number of studies that connect microbial changes with diseases, including obesity, diabetes, asthma, and even possibly autism. In some cases where people have chronic infections such as hepatitis C, bacteria that belong in the intestines have migrated out to the spleen and liver, he said, where they may be doing harm. There’s also evidence that friendly microbes have migrated to harmful locations in people with a chronic digestive disorder known as inflammatory bowel disease. He considers these “good bugs gone bad.”
By studying mice, he and collaborators have identified the immune cells that keep our good bugs from straying. Called innate lymphoid cells, they are part of the ancient immune system that we share with insects and fish.
In a series of experiments, he and collaborators disabled those cells in mice and found that, indeed, helpful intestinal bacteria escaped to other parts of the body. That situation leads to chronic inflammation. The results were published last week in the journal Science as part of a special series devoted to our resident microbes.
Many interesting questions remain, including whether abnormalities in our bacterial colonies are causing disease, or whether conditions such as diabetes are disrupting our microbes. We and our bacteria are in this together, our evolution forever linked to theirs.
References:
Innate Lymphoid Cells Promote Anatomical Containment of Lymphoid-Resident Commensal Bacteria: http://www.sciencemag.org/content/early/2012/06/05/science.1222551?explicitversion=true
Contact Faye Flam at 215-854-4977, fflam@phillynews.com, or @fayeflam on Twitter. Read her blog at philly.com/evolution.
Great idea for a column as this is something of vital importance to every human being, but about which very few are cognizant. Good job taking complicated ideas and making them as digestible as yogurt with a heaping helping of Lactobacillus (the cited abstract would likely be undecipherable to most).
But I would suggest one tiny change in wording: "Called innate lymphoid cells, they are part of the ancient immune system that we share with insects and fish." This should probably be a ", which" because although the ancient innate immune system is shared with insects, innate lymphoid cells appear (upon my reading of the literature, as I'm no expert on immunology) to be restricted to vertebrates.— anaxyrus- What a great article. I did know that we do, in fact, harbor a myriad of bacteria (good and bad, both with their respective roles), brewing within us. But to learn that some of these little fellows may decide to take a trip and "travel", and the repercussions that ensue when they do, gives me pause, indeed! A little war of "good and evil" brewing in my very own tummy! But the facts completely speak for themselves - so much change has occurred, even within my own (fifty year) lifetime. Many adjustments, on the part of the microbes, to be sure. We are, indeed, in this together, and apparently for the long haul. Thank you, Faye, for a very thought provoking piece!— fineprintJK1
- I'll check on the point made by comment 1 on the innate immue sytem and the innate lymphoid cells. You may be correct on that.— fayeflam
Fascinating on many, many levels!
Scientifically: The nature of ,and history of, this mutually beneficial (symbiotic!) relationship between humans and bacteria.
Philosophically: How wonderful to consider that we each carry "enormous communities" within!
Many thanks Faye!- It’s ironic that I read a similar article from the Scientific American, Jun 2012 “The Ultimate Social Network”. This article also talked about the rise of obesity and autoimmune disorders from not having certain microbes in the stomach. Very interesting. Thanks for the great article. Keep up the great work.— bgh777
- The symbiotic relationships of E. coli. and us can only be by design--more evidence for a creator. How could this complex biology develope in a random step by step process?— Ted Siek
- I dispute that the friendly microbes from the gut would hurt other organs. What if the body sends them there to fight toxins? The toxins in our air, food, and water are far worse for our health than our microbes. Louis Pasteur created too much paranoia about microbes, calling them germs. There are bad microbes, but the friendly ones defeat the bad ones in most circumstances. Certainly in an otherwise healthy body, the microbes would be busy fighting toxins, not creating problems.— organic-cures
- Our symbiotic bacteria had better stay that way. If they turn against us, we are really in deep trouble.— cdarwin
- To Ted Siek:
Before you criticize something, you should make an effort to first understand it. Failure to do so risks appearing arrogant and ignorant.
I'm just a lay person, but I have no trouble imagining how this sybiotic ralationship evolved: When our ancient ancestors swam in the seas they were surrounded by millions of different strains of microorganisms. Just as they do today, these little critters worked their way into every nook and cranny of our aquatic forefathers-and-mothers. Some got into the digestive tracts. Of these, some were harmed or killed by the conditions and thus became irrelevant to this story. Others could survive, but they attacked their hosts. These hosts either died right away or were disadvantaged in living to reproductive age and spawning successfully. These hosts thus could not have been our ancestors. But, some hosts who worked out a winning give-and-take relationship with their little hitch-hikers might have turned out to get a bit more energy from the food they ate - or some other small advantage. THESE hosts thus would have a leg up in the struggle to reproduce. Over hundreds of millions of years, across trillions of hosts and perhaps quintillions of bacteria, these relationships that had the best over-all outcomes for both host and bacteria would get prferential reproductive success. And finally, we arrive at today where we see the results of 99.999999999% of those relationships discarded and only the best retained.— MoarSciencePlz 
Comment removed.
In pursuit of her stories, writer Faye Flam has weathered storms in Greenland, gotten frost nip at the South Pole, and floated weightless aboard NASA’s zero-g plane. She has a degree in geophysics from the California Institute of Technology and started her writing career with the Economist. She later took on the particle physics and cosmology beat at Science Magazine before coming to the Inquirer in 1995. Her previous science column, “Carnal Knowledge,” ran from 2005 to 2008. Her new column and blog, Planet of the Apes, explores the topic of evolution and runs here and in the Inquirer’s health section each Monday. Email Faye at fflam@phillynews.com.
Reach Planet of the at fflam@phillynews.com.
