Being Human | Rob Knight

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Whether we’re fat or thin depends on the bacteria in our gut, says biochemist Rob Knight in this video for the World Economic Forum. It’s our microbes, more than our DNA, that makes us who we are: “I can tell you with over 90% accuracy whether you’re lean or obese based solely on sequencing your microbial genes,” he says. Knight’s lab at the University of California, San Diego is pioneering global research on microbes, and how they may be linked to a range of conditions from anxiety to autism.

Click on the link to watch the full presentation, or read key quotes below.

On exploring our inner ecosystem
“Each of us consists of about 10 trillion cells that carry our genome that we think of as human, but we have inside us as many as 100 trillion microbial cells – tiny organisms too small to see with the naked eye. And our whole human genome consists of about 20,000 genes, depending on what you count exactly. But our microbial gene catalog ranges from two to 20 million microbial genes, and so by that measure we might think of ourselves as less than one percent human.”

“The human microbiome project, which was a huge hundred seventy-three million dollar initiative funded by National Institutes of Health (NIH) to jump-start research on the microbiome, together with a consortium of about 400 other researchers. We mapped the healthy human microbiome and 250 healthy volunteers working at many sites in the body, and the speed with which this escaped the pages of a scientific journals to the cover of Scientific American and then to the cover of The Economist was really dramatic.”

On our unique microbial fingerprint
“We can prove cause-and-effect by using mice. We can raise mice without any microbes of their own, and then transmit to them the microbes of someone who’s fat versus someone who’s thin; what you see is the amount of weight they gain depends on the microbes they got. Additionally we can do this for behavior: you can make a mouse more anxious by giving it the microbes of a more anxious mouse, or less anxious by giving it the microbes of the less anxious mouse. This is really remarkable in the case of obesity which a lot of people attribute to willpower or to our human genes; or in the case of anxiety because what this shows is that microbes can affect these traits that affect how we think of who we are.”

On the potentials of microbial research
“One my colleagues at Caltech has done work on a mouse model that resembles some features of autism, where you give pregnant female mice a chemical that simulates a virus, and then their pups have many dysfunctional features that resemble autism. So they have cognitive deficits, they have social deficits, they have got gut barrier dysfunction, and they have compulsive behavior. Part of the reason for this, is that they have a dysfunctional microbial community that is different from the microbial community of a normal mouse.”

“You can induce the same symptoms by injecting normal mice with one chemical that this altered microbial community produces, and then you can rescue them by giving them a probiotic, a kind of beneficial bacteria isolated from the human gut. This is model work and we do not yet know how it will apply to humans, but the potential for this kind of research to affect a wide range of diseases that you might not have thought were linked to your gut is tremendous. One remarkable fact about the gut microbiome, is (if you think of it as being like an organ) that is the only organ you can transplant without doing surgery.”