Image: Bryan Christie
In Brief
- Bacterial cells in the body outnumber human cells by a factor of 10 to 1. Yet only recently have researchers begun to elucidate the beneficial roles these microbes play in fostering health.
- Some of these bacteria possess genes that encode for beneficial compounds that the body cannot make on its own. Other bacteria seem to train the body not to overreact to outside threats.
- Advances in computing and gene sequencing are allowing investigators to create a detailed catalogue of all the bacterial genes that make up this so-called microbiome.
- Unfortunately, the inadvertent destruction of beneficial microbes by the use of antibiotics, among other things, may be leading to an increase in autoimmune disorders and obesity.
More In This Article
Biologists once thought that human beings were physiological islands, entirely capable of regulating their own internal workings. Our bodies made all the enzymes needed for breaking down food and using its nutrients to power and repair our tissues and organs. Signals from our own tissues dictated body states such as hunger or satiety. The specialized cells of our immune system taught themselves how to recognize and attack dangerous microbes—pathogens—while at the same time sparing our own tissues.
Over the past 10 years or so, however, researchers have demonstrated that the human body is not such a neatly self-sufficient island after all. It is more like a complex ecosystem—a social network—containing trillions of bacteria and other microorganisms that inhabit our skin, genital areas, mouth and especially intestines. In fact, most of the cells in the human body are not human at all. Bacterial cells in the human body outnumber human cells 10 to one. Moreover, this mixed community of microbial cells and the genes they contain, collectively known as the microbiome, does not threaten us but offers vital help with basic physiological processes—from digestion to growth to self-defense.
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36 Comments
Add CommentThe complex relationships between humans and bacteria are fascinating. Many are (at first) horrified to learn that the average person possesses over 100 TRILLION bacteria (including perhaps a billion or more E.Coli) in and on our bodies. Interestingly, our bodies frequently live in symbiosis with these bacteria: for example, bacteria such as E.Coli in our gut synthesize Vitamin K, a vitamin important for blood clotting. Individuals taking certain antibiotics may experience a nearly 3/4 reduction in Vitamin K production. If you'd like to read more on fascinating topics within science, medicine, and technology, feel free to browse my blog: http://biginscience.com/
Reply | Report Abuse | Link to thisWe could also take a different look at it. I am sure, thousands of years back we might not have had the same microbiome. It is ever evolving. Microbes always colonize any organic living tissue for food. And when any microbe first colonized a host, they might have been pathogens and after a long period of fight between host and the pathogen, they co-evolved and thus might've acquired symbiotic form of living together happily. And thus even the use of Vitamin K in hosts biological process could've been after the microbes colonization(may be we didn't have any use for vit.K earlier, but evolved after long time of cohabitation). In the same way, microbiome would certainly differ between different groups of people and would depend on factors like environment, weather, food and even culture. Not to forget the difference between microbiomes in different animals. It is a good scientific improvement, but the question is(based on above mentioned factors) what is the use of such data? Will it be useful to cure diseases or are we complicating ourselves with humongous amounts of useless information? Future scientific improvements might hopefully give us the answer.
Reply | Report Abuse | Link to thisMore than 50 years ago, I was learning in high school that the cow had multiple stomachs and its digestive system made use of bacteria to digest. As even typical today, it never occurred to most then, as now, that what was the case of the cow was also likely similar to us humans, being animals, you see.
Reply | Report Abuse | Link to thisIt was obvious to me then, so these details are not a surprise. It's a surprise that it took so long.
Antoine Béchamp discovered and promoted this fact well over 125 years ago (see "terrain theory"), yet he was ridiculed and dismissed by the scientific community at large in favor of Louis Pasteur - who insisted that a "healthy" human body was completely sterile. So Pasteur's inadequate teachings became the ruling medical paradigm, and Béchamp's considerable body of research was put aside and forgotten. If we had listened to Béchamp, we would have accepted that "the human body is not such a neatly self-sufficient island after all" ages ago and our current progress and understanding would be light years ahead.
Reply | Report Abuse | Link to thisThat would be Antoine *Bechamp (apparently the commenting system doesn't display accented letters)
Reply | Report Abuse | Link to thisInteresting point about Pasteur. I did not know that he thought the body was sterile.
Reply | Report Abuse | Link to thisIt is evident that human life is in symbiosis with bacteria, as well as other environmental agents. The point is how is it possible recognise at the bedside when life is encouraged, or not, by bacteria? In my opinion, the absence of Acute Antibody Synthesis, I described in 1997, is a reliable clinical tool among an awful number of others: Stagnaro-Neri M., Stagnaro S., Semeiotica Biofisica del torace, della circolazione ematica e dell’anticorpopoiesi acuta e cronica. Acta Med. Medit. 13, 25, 1997
Reply | Report Abuse | Link to thisWhy is there so much autism, ADHD, food allergies, asthma?? Changes to the human microbiome (in combination with other environmental factors) is what is leading to an unprecedented number of children developing autism, ADHD, food allergies, asthma and many more chronic conditions in the industrialized world. Yes, imbalances in our microbial ecology are resulting in dysregulated immune systems; What's more, commensal microorganisms are also responsible for helping us to detoxify and eliminate environmental toxins as they enter our bodies (including heavy metals, pesticides, and other chemicals). See Rowland et al., Archives of Environmental Health 39, no 6 (1984):401-8; there are volumes of articles published in the medical literature on this subject. We are raising an entire generation of immunocompromised children because the human microbiome (and thus immune function) has been been altered considerably over the last few decades in America. To learn more, see A Compromised Generation: The Epidemic of Chronic Illness in America's Children www.acompromisedgeneration.com or Epidemic Answers www.epidemicanswers.org
Reply | Report Abuse | Link to thisI have read that there are about 10+13 cells in the human body.
Reply | Report Abuse | Link to thisIf we were to assume there to be ca. 10 times as many bacterial cells in our constitution, that would make ca. 10+14 bacterial cells
If the bacterial cells are about 1/10 the size, & therefore guesstimating to be about 1/10 the weight of a human cell, then the weight of the bacterial cells would be ca. equal to the weight of the human cells.
So a 150 lb person would be 75 lbs "human" and 75 lbs "bacteria".
It would be interesting to know how this number (10 times as many bacterial cells in a human ) was derived.
Any microbiologists reading this thread??
---- each chip, atom, molecule, cell, air, water, matter, the dark matter (energy) of space with its planets and stars are as one and it takes all of this just to move your little finger.
Reply | Report Abuse | Link to thishttp://www.scientificamerican.com/article.cfm?id=the-compass-within
My doctoral thesis work in the 1990's involved host-commensal interactions, and we were generally relegated to the backwaters of the microbiological meetings. It's nice to see that this crucial area of interface biology is finally getting the attention it deserves.
Reply | Report Abuse | Link to thisI read this excellent article. However, I disagree with two ideas that have been expressed in the article as well as in other articles on the subject. While I agree that the bacteria on our bodies are extremely important to protect our health and to contribute to some of our diseases, I question whether the bacteria are on our bodies. They are in our intestines, but the material in our intestines are really outside our bodies (you can think of your intestines as a tube going from your mouth to your anus). Likewise, the surfaces of our mouths and noses are outside our bodies. And, the vagina and other parts of the female genital tract are really outside the body as is the urethra in both males and females. Obviously, the surface of the skin is outside the body, as well.
Reply | Report Abuse | Link to thisSo, any part of our body that has bacteria has the bacteria on it rather than in it. The effects of bacteria on the body are a result of substances, whether it is proteins break-down products of food or vitamins, that are absorbed by our bodies.
However, bacteria in our bodies are almost always a bad thing. When that happens we have an infection, whether it is in the blood or another normally sterile area of our bodies.
So the proper term to describe the relationship of bacteria and our bodies is the bacteria are on our bodies rather than in our bodies. They are, nonetheless, a vital part of our bodies.
The second thing I question is the importance of the number of genes that bacteria have. The article stated that there were 3.3 million genes in the digestive system. I doubt this. There were more than 1000 bacteria species. So that is around 3 thousand genes for each bacteria species. Maybe there are 1000 different versions of some genes (like the 16S ribosomal gene in the article), and hundreds of different versions of other genes, but I really doubt that there are 3.3 million genes in the bacteria pool in our poop (when they say our intestines, they really mean in our feces - that is what is sampled). So, it is much more accurate to say that our intestines may have 1000s of different bacteria and millions of versions of the thousands of genes that all these bacteria carry. It's important to use the scientific terminology very carefully. I know it can be confusing, but using the scientific terminology improperly leads to even more confusion.
Jeff Utz, M.D.
The problem with this is that bacteria are about 0.001 the size of human cells (1/1000th the size). The confusion is that the bacterial cells are about 1/10 as long as human cells. And 1/10 as wide and 1/10 as tall. (So 1/10 times 1/10 times 1/10 is 1/1000).
Reply | Report Abuse | Link to thisMost of the bacterial cells are in our intestines. There's maybe around 4 liters of partially digested food and food waste in our intestines (about 1 gallon with a weight of around 8 pounds). Maybe a pound or two of those intestinal contents is bacteria (every day we pass around a half pound of feces which is about 1/3 bacteria by weight). Add to that the bacteria in our mouths and noses, throats and respiratory tree, on our skin and in our genitourinary tracts. So we have maybe 2 or 3 pounds total of bacteria on us (though not really in us - we don't have bacteria in our blood stream, joints, hearts or brains - that would be bad).
wscovel: Yes, the *diameter* of a typical prokaryotic cell is about 1/10th that of a eukaryotic cell (with a huge range of variation for both). But that means its *volume*, and therefore its weight is about 1/1000th that of a eukaryotic cell. The human body contains a couple of pounds of microbial cells, mostly within the intestines.
Reply | Report Abuse | Link to thisThis excellent article on the human microbiome nicely characterizes the present but misses a bit of historical context. Knowledge about beneficial microbes did not just begin in the 1980s; one reader mentioned Bechamp's work before that. But Metchnikoff, a Russian scientist and contemporary of Pasteur, also knew about beneficial bacteria as far back as the late 1800s. He studied the healthy, long-lived Bulgarian people who regularly consumed lactic-acid-soured milk and investigated the interactions of bacteria with the human immune system. Metchnikoff’s work was largely forgotten, probably because Pasteur’s anti-pathogen pursuits gave the public a better narrative. Pasteur’s work won out, which is the reason that today most people still think bacteria are inherently bad. http://intestinalgardener.blogspot.ca/
Reply | Report Abuse | Link to thisThis excellent article on the human microbiome nicely characterizes the present but misses a bit of historical context. Knowledge about beneficial microbes did not just begin in the 1980s; one reader mentioned Bechamp's work before that. But Metchnikoff, a Russian scientist and contemporary of Pasteur, also knew about beneficial bacteria as far back as the late 1800s. He studied the healthy, long-lived Bulgarian people who regularly consumed lactic-acid-soured milk and investigated the interactions of bacteria with the human immune system. Metchnikoff’s work was largely forgotten, probably because Pasteur’s anti-pathogen pursuits gave the public a better narrative. Pasteur’s work won out, which is the reason that today most people still think bacteria are inherently bad. http://intestinalgardener.blogspot.ca/
Reply | Report Abuse | Link to thisThe evidence keeps mounting that antibiotics are to be used in emergency situations only where the life of the individual is immediately being threatened. Otherwise we wind up indiscriminately killing beneficial microbes as well and causing many undesirable side effects in human health. It now only seems obvious that an attempt to sterilize our bodies from all germs is not the right approach to good health in the long run. The first victim of this new knowledge should be anti bacterial soap for everyday usage. It is just not a smart thing to do any more.
Reply | Report Abuse | Link to thisIt seems that when it comes to antibiotics, anti-bacterial soap, etc there is a fine line between what is beneficial and what is not. This could open up a new field of developing methods of making these products more effective in targeting only certain bacterias, could it not?
Reply | Report Abuse | Link to thisI find it interesting to think about the relationship between this article and the short article "Microbial Mules" also published in this issue. I am curious to know how much the researchers engineering microorganisms to transport nanoparticles and drugs are taking into account the competition their microorganisms will face from others in the body. Or is this not relevant because they will be injected into the blood stream which is sterile and will thus not face any competition?
Also, there was Sci Am online article published in 2007 on this same topic: http://www.scientificamerican.com/article.cfm?id=strange-but-true-humans-carry-more-bacterial-cells-than-human-ones
While Bechamp was correct that there are bacteria in our bodies, and partially correct that the balance of said bacteria could make a person sick or well, he was wrong on other accounts, such as this being the only cause for disease. On that point, germ theory was much more on target. Plus, Pasteur was able to show through experiments (inducing a pathogen and curing the ailment caused by it) that germ theory worked. As far as I know (and I could be wrong) Bechamp could not do this and his main way of testing his hypothesis was by altering the pH levels of the blood, which could cause some serious problems. I would agree that Bechamp's theory should not have been thrown out so carelessly, but to say we would all be better off had we listened to him.....well, I'm not so sure.
Reply | Report Abuse | Link to thisEither way, it's really a moot point now 100 years later.
Just read the article in the paper edition, really fascinating. What I'm wondering is -- how do all these different types of bacteria get into the body in the first place? Especially those that are at home in the gut? Wouldn't they die when exposed to a "normal" environment? Even if they can survive (for some time) in the open air, I'm really curious what's the path that brings them into the bodies of babies.
Reply | Report Abuse | Link to thisThere are other questions I'm left with after reading the article. Do we share (much of the) biome with other mammals, or are most of these bacteria species-specific? Are there things one can do (apart from eating dirt) to improve the bacterial balance in one's body?
"What came first" -- the egg or ---
Reply | Report Abuse | Link to thisThe answer is "NEITHER"! All life produces life and after this life is produced, its environment will determine whether or not this life form will continue as a reproducing species. There is a difference between life and species.
In removing the nail from the shoe of Anthropology I would suggest that if they are serious in discovering the origin of man that some effort is put forth in finding out from which tree, plant or bush we came!
Then when thats accomplished, find the mineral or rock.Oh heck lets just cut to the chase. When someone says your a ball of fire, well, you really really are!
cbc.ca bruce voigt
very enlightening
Reply | Report Abuse | Link to thisGreat Article! I'm definitely a huge believer that we have a symbiolic relationship with Bacteria and that there is such a thing as Beneficial or "Good Bacteria"--
Reply | Report Abuse | Link to thisAfter being on an Anti-Biotic/Cipro for about a month,I started having constant digestive problem--Bloating, Cramps,and D. The symptoms continued for about a year-- Only to be told by my Dr. that I now had "IBS"--
After watching a Documentary on Probiotics, it be became very clear that there is some very strong scientific evidence suggesting that Probiotics can make a huge difference in helping with GI and Allergy related Problems!
I am hoping some one out there will answer your query,
Reply | Report Abuse | Link to thisThat particular aspect had not occured to me and now I cant get it our of my head, it is like the song that will not go away, LOL. Hope some one can help
I am hoping some one out there can answer your query, I had never thought of that aspect of things, now it is stuck in my head, like that tune that will not go away, LOL
Reply | Report Abuse | Link to thisDid you miss the part of most of the cynobacteria in the stomach being what assist in metabolizing. The inside of the stomach is certainly inside the body.
Reply | Report Abuse | Link to thisThe point I think you and probably most I am unique people are missing and what for some reason a philosopher saw over 2400 years ago is that all systems are intertwined. Siddhartha did all he could to destroy the concept of self, he would have loved this article and any believer of the concept of Gaia and that includes some pretty good thinkers (Freeman Dyson for one) can see that each system is interdependent on another system.
The concept of self may really be no more than a concept of resolution, that those little bugs go with this unit and those other little bugs go with that unit and these units go with a bigger unit (Earth) and that unit goes with something bigger (solar system) and that system goes with something bigger (galaxy) and that system goes with something bigger (universe) and that system goes with something bigger (multi-verse) and all the systems together create one big system.
I found the article very enlightening in that I always considered the body more of a condominium for supporting other life. A good analogy is that more life comes from a dead tree than a live one, but evolution works in its own way and by trying this piece and that piece eventually the pieces fit together.
Now as we destroy green ways, bio systems, ecosystems and all the other feedback systems, then you my friend will find the folly in a world only tarnished on the outside.
Regarding bacteria that is bad for us, again give evolution some credit as the article states there are TCells and antiTcells that balance the effect so that if an invasive species enters and causes distress it is dealt with. In fact the problem we have imposed on our selves based on thinking like yours is we have destroyed our autoimmune's system to differentiate between the two and now have the body attacking itself when perhaps that is the last thing it should do.
Also consider some of the relationships took millions of years and not just enter, jiggle, wiggle and ready to go. As we often see with virus and bacteria infections over time the effects become less adverse and often symbiotic. Billions of years is a very very long time for living organisms to become friends.
Ranchers feed cattle enormous quantities of antibiotics because it makes them gain weight. The assumption is that the antibiotics keep cattle healthy, but maybe they keep them hungry.
Reply | Report Abuse | Link to thisIt's a fascinating idea that the childhood obesity epidemic may have more to do with over-active medicine than under-active kids. And it would probably be easier to moderate the antibiotics than to pry kids away from their computer games.
An enlightened individual. I came to this article after asking my professor how it was that the intestinal system of an infant (at one time sterile) became colonized. He, the anatomy prof. and my micro. prof., both said through external bacteria - the feces at birth, the breast feeding, and vaginal flora when passing through the canal.
Reply | Report Abuse | Link to thisFor starters, 1/3 of the pregnancies are c-section. A lot of women don't breast feed. And I delivered some babies on rotation so I know that feces is kept south of the vagina. This explanation, and that they put things in their mouth growing up doesn't explain the countless different organisms. I can guarantee that if you went around swabbing everything a child could get their hands on, you won't find many of the enteric bacteria in culture.
I believe in spontaneous generation out of the microzyma theory. It only makes sense given that we are a microcosm of the macrocosm, and withing us, is then the microcosm of the macrocosm, which now us. There is a field of infinite potential and when morbid matter accumulates, I believe there are microbes that are born, if not already there, which break down this waste material.
If you leave dirty dishes and food laying around, what comes out? The bugs to clean up your trash. It happens everywhere. Why would it not happen in the body? Mainly speaking of parasites here. Even if one doesn't want to believe in spontaneous generation, I think the principle is the same which at the very least should illustrate that it is not the bugs that are the cause of our illness, but the decreased vitality of the individual.
A healthy person does not get sick. This has been shown by old time naturopaths who swallowed vials of cholera, rubbed small pox on their body and didn't get sick. They've swabbed the mouths of infants and found diptheria, but yet the child was not sick.
An enlightened individual. I came to this article after asking my professor how it was that the intestinal system of an infant (at one time sterile) became colonized. He, the anatomy prof. and my micro. prof., both said through external bacteria - the feces at birth, the breast feeding, and vaginal flora when passing through the canal.
Reply | Report Abuse | Link to thisFor starters, 1/3 of the pregnancies are c-section. A lot of women don't breast feed. And I delivered some babies on rotation so I know that feces is kept south of the vagina. This explanation, and that they put things in their mouth growing up doesn't explain the countless different organisms. I can guarantee that if you went around swabbing everything a child could get their hands on, you won't find many of the enteric bacteria in culture.
I believe in spontaneous generation out of the microzyma theory. It only makes sense given that we are a microcosm of the macrocosm, and withing us, is then the microcosm of the macrocosm, which now us. There is a field of infinite potential and when morbid matter accumulates, I believe there are microbes that are born, if not already there, which break down this waste material.
If you leave dirty dishes and food laying around, what comes out? The bugs to clean up your trash. It happens everywhere. Why would it not happen in the body? Mainly speaking of parasites here. Even if one doesn't want to believe in spontaneous generation, I think the principle is the same which at the very least should illustrate that it is not the bugs that are the cause of our illness, but the decreased vitality of the individual.
A healthy person does not get sick. This has been shown by old time naturopaths who swallowed vials of cholera, rubbed small pox on their body and didn't get sick. They've swabbed the mouths of infants and found diptheria, but yet the child was not sick.
That is beautifully said, can I quote you on that passage?
Reply | Report Abuse | Link to thisEat fermented and raw organic or best, wild foraged food. That is the best place to get your bugs!
Reply | Report Abuse | Link to thisThat is beautifully said, May I quote you on that passage?
Reply | Report Abuse | Link to thisA problem arises when we talk about things being 1/10th the size. If we're talking about volume that's fine but if we're talking about a measure of length then the volume is actually 1/1000th and are weight measurement is greatly reduced. I pulled a few "average" cell size numbers to better help, I was curious myself how weight I'm carrying around. Keep in mind average is pretty loose here. The average human cell is 10 um so assuming a spherical (not likely but with only one dimension doesn't assume anything more) shape we get V=(4/3)pi()r^3=(4/3)pi()5^3=523.6 um^3. The average size of an average bacterium I found listed between 0.6 and 0.7 um^3 and for the sake of overestimating I used 0.7 um^3. With 10 of them per human cell the volume fraction is (0.7 um^3 * 10)/(0.7 um^3 * 10 + 523.6 um^3) = 0.0132 or 1.32% multiplying by 150 lbs we get 1.98 lbs of bacteria.
Reply | Report Abuse | Link to thisWe can get some form of loose validation from the fact that with 10^14 human cells in the average adult human and the 10:1 bacteria to human cell ratio we have 10^15 bacteria. Another source lists 10^12 e. coli (referred to as "average sized bacteria") to weight 1 gram. So 10^15 bacteria / 10^12 bacteria/gram = 1000 grams = 1 kg = 2.2 lbs which is pretty darn close to 1.98 lbs!
Of course this doesn't take the more incorporated ones (mitochondria) into account as we've already grown accustomed to calling them 'us'.
I think that considering that I'd die without them I'll continue to carry around my 2 pounds of strange friends. The next time somebody says you should lose 2 pounds make sure it's not these guys.
P.S. The 2-3 pounds of bacteria from the feces calculation by jputz is wonderful. I lack that depth of knowledge about poo so I defer to your expertise on the subject and remain satisfied with the thought that everyone seems to agree that it's only a few pounds we carry about depending, somewhat, on the exact time of day. ;)
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