Photosynthetic humans--endowed with the power to derive energy from the sun--are a popular construct of science fiction. But Pamela Silver, a biologist at Harvard Medical School, aims to push that concept into reality.

Silver's research focuses on cyanobacteria, a microbe responsible for almost 50 percent of the earth's photosynthetic ability. Her team aims to harness the organisms' photosynthetic powers by engineering them to generate fuel and other valuable chemicals.

But Silver is also experimenting with a more fantastical use for the microbes. In a recent experiment, researchers injected fluorescently labeled cyanobacteria into zebrafish embryos, a species commonly used in research. The fish are transparent, making them easy to observe during development. Much to Silver's surprise, the fish survived and grew, as did the fluorescent microbes living inside their cells. "When we put E. coli into fish, they blew up, but they are extremely tolerant of cynabacteria," Silver said at a synthetic biology conference in Boston last week, where she presented the research. Right now, the system doesn't make enough energy to maintain the fish, but the researchers are experimenting with different engineering approaches to enhance production.

The video below shows Zebrafish embryos (green) that have been injected with photosynthetic cyanobacteria (red).

The ability to run on sunlight would certainly be a handy superpower. But what if you still like to eat? James Liao, a biologist at UCLA, has developed a new strategy to enhance cells' ability to burn fat by adding a metabolic pathway from bacteria and plants. (For more details, see Making Fat Disappear.) "Female mice show a huge decrease in diet-induced obesity, and they accumulate much less fat," said Liao at the conference. Results for male mice are less dramatic, though it's not clear why.

A family tree showing representatives of the major groups (phyla) of microbes in different colors. Names in red are the first 56 genomes sequenced for the Genomic Encyclopedia of Bacteria and Archaea. This group represents a broader sampling of the "Tree of Life" than has previously been achieved. For a high resolution version, click here. Credit: Jonathan Eisen, UC Davis

A newly mapped section of the tree of life showcases the genomes of more than 50 microbial species. Researchers say the comprehensive catalogue of genomes--just the first chapter in a larger project--will help them find new genes and predict their functions. The research was published today in the journal Nature.

The planet houses an estimated nonillion--10³⁰--prokaryotic microbes, organisms that lack a cell nucleus. According to a press release from the University of California, Davis, only about a thousand of these have been sequenced to date, mostly those that cause disease or have potential industrial applications, such as producing biofuels.

"That's like making a map of the world and only mapping three cities," said Jonathan Eisen, a microbiologist at the UC Davis Genome Center and the U.S. Department of Energy Joint Genome Institute, in the statement. According to the release:

The new study, called the Genomic Encyclopedia of Bacteria and Archaea or GEBA, looks instead at representatives from across the major branches of the family tree of microorganisms.

The study shows that although microbes are known to swap genes with other species (a process called "lateral transfer,") phylogeny, or position on the family tree, is more important in determining where new genes appear and how they spread.

"Lateral transfer does not shuffle evolutionary innovations in a massive way," Eisen said. "If there is an innovation in a branch, you tend to find it in the same branch downstream."

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."