Our Bacterial Selves

 

   

 

 I start many conversations with "There are 10 times more bacterial cells than human cells living in us and on us. We are more bacterial than human." 

 

But as newborns, we come into this world sterile. It is by passing through the vaginal canal that provides our first dose of bacteria, called lactobacillus. Right out of the gates, bacteria gifts us with the ability to digest our mother's milk. 

 

That's day one. How does bacteria help us for the rest of our lives?

 

Scientists have studied bacterial DNA from healthy individuals and found 10,000 DIFFERENT species of bacteria. To put that number into perspective, many probiotics boast on having 10 to 20 species. Lame.

It's time we learn more about our "bacterial selves".

 

Studying our bacterial selves has only recently been possible as a result of the genome revolution (See post below). Cells from our mouth, genitals, gut, nose, skin, and even belly button have been sequenced. Strikingly, for every human gene there are 360 bacterial genes. I find this both exciting and frightening. Imagine going to a mechanic who only knew how 0.2% of a car worked.  Now replace that mechanic with a doctor, and replace that car with you!

 

For better or for worse, funding is largely given to scientists that study what's killing us. Cancer and pathogenic (bad) bacteria or viruses always take center stage and a good chunk of funding. The 10,000 bacteria that make us who we are have been watching from the peanut gallery.

 

Healthy bacteria equals a healthier you, and scientists are studying how to enrich the good guys, while minimizing the impact of bad ones. Imagine a house party where every time a crasher tries to join in, the host uses mustard gas.  The crashers are killed, but so are your invited guests. In later parties, the crashers get wise and bring masks. Now everyone dies, except for the evolved party crashers. When we get an infection, we drop antibiotic bombs on the bacterial party in our guts; killing the good guys that brought the keg, chips, and dip. By learning more about the good bacteria, we can start treating infections with snipers instead of bombs.

 

So what do our bacterial selves do? The easier question might be what don't they? Alterations in our bacteria have been linked to Crohn's and irritable bowel syndrome. That may not come as a surprise, but links are also being made to our behavior, depression, allergies, and many, if not most, inflammation-related diseases.

 

One of the key goals of the study was to find the key bacteria in all healthy individuals. Shockingly, it turns out that different people have different microbial communities, and so do different body parts on the same person! Not a single species was universally present across all volunteers. This suggests different bacteria can do the same jobs. We have to find out what those jobs are. What causes the bacterial diversity? Age, gender, weight, diet, geography, genetics, the tenancy to lick door knobs? These and more likely play a role.

 

Sequencing an individuals bacteria again after several months showed the same bacterial communities. This means our bacterial selves are unique, but stable over time. I can easily imagine a future where a visit to the family doctor will literally involve a "gut check".  When you are young and healthy, your stool sample will be used to grow, dry and store your bacterial selves in pill-form. You'll then be able to rePOOPulate your gut for the rest of your life and whenever you want - after a dose of antibiotics, traveler's diaherra, or any other illness.

The Human Microbiome Project Consortium, “Structure, function and diversity of the healthy human microbiome,” Nature, 486: 207-214, 2012.