Not Entirely Human?

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'We are not entirely human'

Washington - We may not be entirely human, gene experts said on Thursday after studying the DNA of hundreds of different kinds of bacteria in the human gut.

Bacteria are so important to key functions such as digestion and the immune system that we may be truly symbiotic organisms - relying on one another for life itself, the scientists write in Friday's issue of the journal Science.

Their findings suggest that studying bacteria native to our bodies may provide important clues to disease, nutrition, obesity and how well drugs will work in individuals, said the team at The Institute for Genomic Research, commonly known as TIGR, in Maryland.

"We are somehow like an amalgam, a mix of bacteria and human cells. There are some estimates that say 90% of the cells on our body are actually bacteria," Steven Gill, a molecular biologist said.

"We're entirely dependent on this microbial population for our well-being. A shift within this population, often leading to the absence or presence of beneficial microbes, can trigger defects in metabolism and development of diseases such as inflammatory bowel disease."

Scientists have long known that at least 50% of human faeces, and often more, is made up of bacteria from the gut. Bacteria start to colonise the intestines and colon shortly after birth, and adults carry up to 100 trillion microbes, representing more than 1 000 different species.

They are not just freeloading. They help humans to digest much of what we eat, including some vitamins, sugars, and fibre. They also synthesise vitamins that people cannot.

"Humans have evolved for million of years with these bacteria. And they provide essential functions," Gill said.

Germ surprise

Gill and his team sequenced the DNA in faeces donated by three adults. They found a surprising amount of it came from bacteria.

They compared the gene sequences to those from known bacteria and to the human genome and found this so-called colon microbiome - the entire sum of genetic material from microbes in the lower gut - includes more than 60 000 genes.

That is twice as many as found in the human genome.

"Of all the DNA sequences in that material, only one to five percent of it was not bacterial," Gill said.

"We were surprised."

They also found a surprising number of Archaea, also known as archaebacteria, which are genetically distinct from bacteria but which are also one-celled organisms often found in extreme environments such as hot springs.

The donors were healthy adults. None had taken antibiotics for a year, as these drugs are known to disturb the bacteria in the body.

Gill said his team hopes now to make a comparison of the gut bacteria from different people.

"The ideal study would be to compare 20 people, 30 people from different ethnic backgrounds, different diets, drinkers, smokers, and so on, because I think there are going to be distinct differences," Gill said.

--A

[Loredoctor]

Still, what is 'human'? Genetically, these results throw the idea of human being identified by DNA, but perhaps humans are the gestalt of all cellular components.
Interesting read, Avatar.

[Avatar]

Agreed on both counts.

And if our gene's aren't "human" it may raise some interesting issues.

Regardless, I agree with the idea of a gestalt...something greater than the sum of its parts.

--A

[Loredoctor]

And if our gene's aren't "human" it may raise some interesting issues.

Well, technically the genes involved in reproduction are "human". But if we look at the issue of the gestalt "human", then genes of prokaryotes are still "human" (in a vague sense).

What really excites me is that they found lots of Archaea. That's very very cool.

[dlbpharmd]

Good article! Makes alot of sense to me.

[Prebe]

A side effect of the need for many beneficial bacteria is that children born by C-section instead of the vaginal way have poorer immune systems. Simply because they didn't start their life by swallowing a mouthfull of s*it and crutch-sweat

[Avatar]

That's interesting Prebe. Had no idea.

--A

[stonemaybe]

Gill and his team sequenced the DNA in faeces donated by three adults

I think I'd like to make a donation to this research

Surely this must have been researched before? If not there's probably a whole new medical speciality here. Not to mention quite a few new 'medical' quackeries (like those pro-biotic drinks).

[Prebe]

...at least that's the theory, I should have added. The statistically worse immune system in C-section babies has not been causaly linked to the presence/absence of any certain bacterial group.

Anywho, my kid is 18 months (he's C-section kid) and he's had only three sick days home from daycare in the first six moths, somewhat below average. Hey! What am I doing? Speaking against a general statistics because I happen to know of an exception? Somebody kick my ass

[wayfriend]

The study is new, but I've been hearing that "humans" are symbiotes for quite some time. Certainly the necessity of bacteria is well known.

There is also discussion as to whether any multi-celled organism is actually a symbosis - that cells are individual organisms that cooperate to survive.

After all, if you are collection of micro-organisms, is it really relevant which ones are derived from which genes? Or which genes are called "human"?

It makes me really wonder what it is that is "me". "I" may be a colony of millions of individual tiny lives.

[aTOMiC]

Well one thing struck me after reading this article. None of us should ever feel totally alone. We have a few friends along for the ride. I wonder if the bacteria living inside us is responsible for the "voices" one hears from time to time.

[wayfriend]

... I wonder if the bacteria are wondering what those voices are that they hear from time to time.

[Prebe]

Actually it is perfectly possible to have a mamal (I don't think it's been tried with humans, but mice and pigs) without any symbionts. They might not feel too cool, but they can easily survive. It's not like the symbioses of mamals are obligate.

Just thought you'd like to know

[Sandgorgon rider]

Certain organelles in plant and animal cells, cloroplasts and mitochondria, have their own DNA and have many characteristics of bacteria. It is theorized that way back these were actually parasitic bacteria of other early cells and that gradually the relationship became symbiotic and eventually they became permanently incorporated into the cell structure essentially becoming part of the plants and animals.

[Prebe]

Absolutely SGR, but that's an entirely different story from symbiotic gut bacteria.

[Loredoctor]

Well one thing struck me after reading this article. None of us should ever feel totally alone. We have a few friends along for the ride. I wonder if the bacteria living inside us is responsible for the "voices" one hears from time to time.

Read Greg Bear's Blood Music. It's absolutely phenomenal.

[wayfriend]

Absolutely SGR, but that's an entirely different story from symbiotic gut bacteria.

I disagree. It's very interesting, in fact. It means that a symbiosis can actually graduate to a condition where the DNA of the different species becomes conjoined - two species becomes one.

I wonder if cell differentiation (still largely unexplained AFAIK) can be traced back to two species sharing DNA.

[Prebe]

Wayfriend: Genes have switched from the ENDOsymbionts to the genomic DNA of humans, and vice versa. But endo symbionts (inside the cell envolope) is still a very much different story from the gut bacteria. Whether you agree or not

Example: Endosymbionts (organelles), such as mitochondria, can't reproduce outside the cell (because of gene complementation). The symbiotic gut bacteria can, given the right chemical circumstances.

And humans can, given the propper circumstances, easilly exist without gut bacteria. But we can't exist without mitochondria.

The story of the endosymbionts is WAY older than multicellular organisms. The endosymbionts are thought to have been internalised by unicellular organisms long before they developed into multicellular organisms.

[wayfriend]

That's a very interesting post. I rest my case.