Here’s my weekly column, which will also run in Monday’s Health and Science section of the Philadelphia Inquirer
Image is from Penn and reportedly shows a color enhanced tissue section from a healthy mouse. The mouse cells are green and bacterial cells are purple.
Next time your digestive system malfunctions in some embarrassing way, you can always blame man’s best friend – not the dog, but the bacterial cells that live in your intestines. Not everyone has a dog but we all have enormous communities of bacteria that help us digest food. They don’t always do a perfect job, but without them we’d have trouble surviving.
In fact, our bodies have about ten times as many bacterial cells as human cells, said David Artis, a microbiologist at the University of Pennsylvania. “Some people have even joked that if one considers the meaning of life,” he said, “it could boil down to us being vessels to carry around bacteria.”
Artis has been studying our relationship to our resident microbes, the vast majority of which live in our intestines. Recently, he’s focused on how they know to be so friendly and refrain from spreading around the body and making us sick.
He’s found these so-called commensal bacteria aren’t friendly by nature. If that enormous load of intestinal bacterial cells got out into other parts of the body, “they could kill us,” he said. Luckily, our immune systems have evolved the ability to police these bugs, keeping them from spreading beyond the intestines, he said. It’s a constant process of negotiation between our cells and theirs. When that symbiotic harmony breaks down, good bacteria can escape and make us sick.
All animals carry around symbiotic bacteria, said Rob Knight, an evolutionary biologist at the University of Colorado, Boulder. Bacteria are good at living with other organisms, and our relationship with them probably predated the origin of the animal kingdom some 600 million years ago.