Learn about the bacteria, fungi and other micro-organisms that maintain human health.
| May 15, 2012 | 14
The body contains 10 times more bacteria, fungi and other micro-organisms than human cells. Most of these species are harmless—although they can still cause illness if they wind up in the wrong place. In addition, researchers are beginning to learn exactly how some microbial species in the body help digestion and contribute to regulation of appetite and the immune system.
Illustration by Bryan Christie
See what we're tweeting about
Deadline: Jun 29 2013
Reward: $7,000 USD
The Seeker for this Challenge desires proposals for chemical methods that could rapidly degrade a dilute aqueous solution
Deadline: Jul 14 2013
Reward: $1,000,000 USD
This is a Reduction-to-Practice Challenge that requires written documentation and&
Powered By: 
YES! Send me a free issue of Scientific American with no obligation to continue the subscription. If I like it, I will be billed for the one-year subscription.
14 Comments
Add CommentThis is an interesting and probably unanswerable question. If all cells weighed the same, the bacteria, fungi and other microbes in a 160 lb. (~73 kg) human, assuming a 10 to 1 ratio in favor of the non-human organisms, would weigh 144 lb. (~65 kg). This seems to me unlikely. Additionally if mitochondria is factored in, which likely is an ancient intruder, an uninfected human would weigh something like the approximate amount of a newborn baby. I am looking forward to comments on this by others having more knowledge than my simple calculations.
Reply | Report Abuse | Link to thisIt is unlikely because in your described calculations you assume that all cells weigh the same. In reality, prokaryotic cells (bacteria) are far smaller than eukaryotic cells (human cells). prokaryotic cells are usually 1-10 micrometers across, whereas eukaryotic cells are usually 10-100 micrometers across. Furthermore, there is a fair amount of weight that is not comprised of cells, extracellular matrix such as that in cartilage and in bone. Even when factoring in mitochondria, the vast majority of the mass of a human is strictly human, that is to say the product of our DNA.
Reply | Report Abuse | Link to thisProkaryotic cells are about an order of magnitude smaller than eukaryotic ones. Also, we have a lot of non-cellular material that makes up our body that doesn't count towards the number of "us" cells.
Reply | Report Abuse | Link to thisActually very little. All of your body, minus your GI tract, mouth, skin, and nasal passages, is generally sterile. That's not to say that this isn't impressive, just misleading.
Reply | Report Abuse | Link to thisI'm not sure that mitochondria should be counted here, as they are such ancient (and essential) commensals they should be regarded as "us". I've seen estimates of several Kg of microbia in the gut making up the bulk of feces.
Reply | Report Abuse | Link to thisFascinating article. Mindful of the possible role of H. Pylori in controlling obesity, and the fact that this commensal bacteria is now absent in the microbiome of so many younger people, are you aware of any efforts to introduce it? Could this become a new Probiotic?
Reply | Report Abuse | Link to thisHere 1:10 is just about the cell count not about the mass of the cells...
Reply | Report Abuse | Link to thisIn the last episode of his excellent "Meet the Scientist" podcast, Carl Zimmer talks with Martin Blaser about H. pylori and the possible reasons and consequences of its disappearance in the human microbiome. Highly recommended - check it out: http://blogs.discovermagazine.com/loom/2010/12/30/losing-our-germs-my-last-podcast/
Reply | Report Abuse | Link to thisJust 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?
Reply | Report Abuse | Link to thisThere are good and bad bacteria and viruses. Proper hand washing with soap and water kills most. Dishes and laundry need to be cleaned with hot soapy water and rinsed well. The dryer kills most harmful ones.
Reply | Report Abuse | Link to thisBlood and body fluids are always to be considered contaminated.
When I was a Nurse in California, one doctor said place a small amount of triple antibiotic ointment in your nose before you go into public to stop mersa.
Kissing and sex spread many germs and viruses.
Clothing carries many of these from person to person.
As a retired Nurse I know this is not true. Many people carry diseases many years with no symptoms.
Reply | Report Abuse | Link to thisI'd question the inclusion of mitochondria as well. We are driven by our metabolic processes to feed our hungry brains. The mitchondria lines we have are absolutely integral to the development of a human.
Reply | Report Abuse | Link to thisSounds frightening...Glad i dont think those thoughts.
Reply | Report Abuse | Link to thisI recently read Michael Pollan's thought provoking article on the health benefits of the human micro biome, and your letter urging caution regarding the risk of systemic sepsis from intestinal luminal breaches.
Reply | Report Abuse | Link to thisI tried unsuccessfully to get a clarification from Pollan and from the NYT; I hope you can help.
When I first read Pollan in the NYT Magazine of May 20th, there was just one area of evidence that I was unable to discern: whether he (or you) had encountered a dose-response relationship, one criteria for causation, for beneficial gut micro biome. The question arose of whether the greater burden of good enteric bugs gave rise to better health than those with less habitat for the same balanced bio-ecology e.g. after a colectomy
My comment follows:
The richness, health and biodiversity of the human gut microbiome could well play a role in favorable immunomodulation required to suppress harmful inflammatory and allergic processes. Ecological disruption of balanced gut microbiome is implicated in the pathogenesis of necrotizing enterocolitis in preterm infants and inflammatory bowel disease in adults, both of which when severe, requires resection of large portions or the whole of the colon. Surgery leads to the life-long loss of habitat for health-sustaining microbial communities. Even if remaining balanced in type and distribution, the microbiome in such individuals are now restricted to short segments of gut that remain. A finding that a healthy but vastly reduced microbial population predisposes to chronic disease compared with a full microbiome complement in people with intact colons reinforces the importance of our microscopic companions for human wellbeing, suggestive of dose-response benefit of the human gut microbiome
Dr Joseph Ting, MBBS; London UK