The back of your knee probably has more microbes than your mouth or your gut--that's just one of the somewhat disturbing revelations from a study published today online in Science. Researchers from the University of Colorado, Boulder have developed the most complete map yet of the microbes that dwell on and in us. "The highest diversity skin sites were the forearms, palm, index finger, back of the knee and sole of the foot. The armpits and soles of the feet showed some similarities, perhaps because they are from dark and moist environments," said Noah Fierer, one of the study's authors, in a statement.

Scientists are mapping our microbial inhabitants in order to better understand their role in human health and disease. As I noted in a previous feature:

Each of us contains roughly 10 times as many microbial cells as human ones. And while some microbes make us sick, many play vital roles in our physiology. They give us the ability to digest foods whose nutrients would otherwise be lost to us, and they make essential vitamins and amino acids our bodies can't. And yet, because the vast majority of these microbes die when extracted from their native habitat, they have been impossible to study and have remained a mystery...

New ultrafast DNA-sequencing technologies allow scientists to study the genetic makeup of entire microbial communities, each of which may contain hundreds or thousands of different species. For the first time, microbiologists can compare genetic snapshots of all the microbes inhabiting people who differ by age, origin, and health status. By analyzing the functions of those microbes' genes, they can figure out the main roles the organisms play in our bodies.

The new study, which analyzed 27 sites on the body of nine different volunteers, found that microbial diversity varies highly, both between individuals and from place to place in the same person. According to a release from the University of Colorado, Boulder:

The study showed humans carry "personalized" communities of bacteria around that vary widely from our foreheads and feet to our noses and navels, said CU-Boulder's Rob Knight, senior author on the paper. "This is the most complete view we have yet of the microbial side of ourselves, one that our group and others will be adding to over the coming years," said Knight, an assistant professor in CU-Boulder's chemistry and biochemistry department. "The goal is to find out what is normal for a healthy person, which will provide a baseline for further studies to look at people with diseased states. One of the biggest surprises was how much variation there was from person to person in a healthy group of subjects."

"We have an immense number of questions to answer," said Fierer, an assistant professor in CU-Boulder's ecology and evolutionary biology department who was a co-author on the study. "Why do healthy people have such different microbial communities? Do we each have distinct microbial signatures at birth, or do they evolve as we age? And how much do they matter? We just don't know yet."

Researchers in Canada have created a solar-powered micro-machine that is no bigger than the period at the end of this sentence. The tiny machine can carry out basic sensing tasks and can indirectly control the movement of a swarm of bacteria in the same Petri dish.

Sylvain Martel, Director of the NanoRobotics Laboratory at the École Polytechnique de Montréal, previously showed a way to control bacteria attached to microbeads using an MRI machine. His new micro-machine, which measure 300x300 microns and carry tiny solar panels, will be presented this week at ICRA '09 in Japan.

On such a small device there is little room for batteries, sensors or transmitters. So the solar cell on top delivers power, sending an electric current to both a sensor and a communication circuit. The communication component sends tiny electromagnetic pulses that are detected by an external computer.

The sensor meanwhile detects surrounding pH levels--the higher the pH concentration, the faster the electromagnetic pulses emitted by the micro-machine. The external computer uses these signals to direct a swarm of about 3,000 magnetically-sensitive bacteria, which push the micro-machine around as it pulses. The bacteria push the micro-machine closer to the higher pH concentrations and change its direction if it pulses too slowly. This is more practical than trying to attach the bacteria onto the micro-machines, says Martel, since the bacteria only have a lifespan of a few hours. "It's like having a propulsion engine on demand," he says.

Martel suggests that micro-machines could one day be used for medical purposes although there's still a long way to go.

The video below shows 3,000 bacteria maneuvering a V-shaped robot around via computer control.