Carl Zimmer on microbes in us

How Microbes Defend and Define Us . Excerpts in reverse order:
"We continue to be colonized every day of our lives. “Surrounding us and infusing us is this cloud of microbes,” said Jeffrey Gordon of Washington University. We end up with different species, but those species generally carry out the same essential chemistry that we need to survive. One of those tasks is breaking down complex plant molecules. “We have a pathetic number of enzymes encoded in the human genome, whereas microbes have a large arsenal,” said Dr. Gordon.

In addition to helping us digest, the microbiome helps us in many other ways. The microbes in our nose, for example, make antibiotics that can kill the dangerous pathogens we sniff. Our bodies wait for signals from microbes in order to fully develop. When scientists rear mice without any germ in their bodies, the mice end up with stunted intestines.

In order to co-exist with our microbiome, our immune system has to be able to tolerate thousands of harmless species, while attacking pathogens. Scientists are finding that the microbiome itself guides the immune system to the proper balance."
"Some microbes can only survive in one part of the body, while others are more cosmopolitan. And the species found in one person’s body may be missing from another’s. Out of the 500 to 1,000 species of microbes identified in people’s mouths, for example, only about 100 to 200 live in any one person’s mouth at any given moment. Only 13 percent of the species on two people’s hands are the same. Only 17 percent of the species living on one person’s left hand also live on the right one."
And a case history:
"In 2008, Dr. Khoruts, a gastroenterologist at the University of Minnesota, took on a patient suffering from a vicious gut infection of Clostridium difficile. She was crippled by constant diarrhea, which had left her in a wheelchair wearing diapers. Dr. Khoruts treated her with an assortment of antibiotics, but nothing could stop the bacteria. His patient was wasting away, losing 60 pounds over the course of eight months. “She was just dwindling down the drain, and she probably would have died,” Dr. Khoruts said.

Dr. Khoruts decided his patient needed a transplant. But he didn’t give her a piece of someone else’s intestines, or a stomach, or any other organ. Instead, he gave her some of her husband’s bacteria.

Dr. Khoruts mixed a small sample of her husband’s stool with saline solution and delivered it into her colon. Writing in the Journal of Clinical Gastroenterology last month, Dr. Khoruts and his colleagues reported that her diarrhea vanished in a day. Her Clostridium difficile infection disappeared as well and has not returned since."
P.S. More in Everyone poops his or her own viruses .
P.P.S. Related : The Evolution of Cooperation by Dave Munger

Update from Carl Zimmer on July 20 The Microbiome Never Ceases to Amaze
It is surprising that nobody metioned Morarji Desai so far.