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EXTRAORDINARY ORGANISMS-The cyanobacterium, Trichodesium thiebautii, form filaments (bottom image) that contain many individual disk-shaped cells, each about 15 micrometers (10-6 meters) wide. Hundreds of T. thiebautii filaments join to create a macroscopic colony about 2.0 millimeters (10-4 meters) in diameter (top image). (Photos by John Waterbury, WHOI)

Cyanobacteria:
Giving Us the Oxygen of Life

Without the cyanobacteria, the life we see around us, including humans, simply wouldn’t be here. Overlooked in the ocean until the 1970s, cyanobacteria are among Earth’s most important organisms

Woods Hole Oceanographic Institution, by John Waterbury  —  One group of bacteria-the cyanobacteria-has completely transformed Earth’s environment through their long history. Three billion years ago, ancestors of cyanobacteria infused Earth’s ancient atmosphere with the byproduct of their photosynthesis-oxygen-changing the chemistry of the planet and setting the stage for entirely new oxygen-breathing life forms to evolve. Without the cyanobacteria, the life we see around us, including humans, simply wouldn’t be here. Overlooked in the ocean until the 1970s, cyanobacteria are among Earth’s most important organisms 

Before 1970, cyanobacteria were known to occur widely in fresh water and terrestrial habitats, but they were thought to be relatively unimportant in the modern oceans. This perception changed dramatically in the late 1970s and 1980s with the discovery of photosynthetic picoplankton by scientists at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology.

Tiny members of this group of newly discovered cyanobacteria, Synechococcus and Prochlorococcus, turn out to be the most abundant organisms on the planet today. They are at the base of the ocean’s food chain, making air, light, and water into food for other life. Today, exploiting new biotechnological techniques, we are exploring their genes and uncovering the secrets of these extraordinary organisms.

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BARBELL BACTERIUM-Cyanobacteria have mechanisms that allow two antagonistic physiological processes to coexist in the same organism: oxygen-producing photosynthesis and dinitrogen fixation, which is inhibited by oxygen. In Richelia (above), the two processes are separated by space: Dinitrogen fixation occurs only in the bulbous, specialized cells (heterocysts) at the end of a 60-micrometer-long, filamentous cyanobacterium. (Photo by John Waterbury, WHOI)

Cycles of life
Bacteria take up the elements essential to life-especially carbon and nitrogen-and incorporate them into molecules that higher bacteria-consuming organisms use for growth. Bacteria also can reverse the transformation, returning elements to the environment, completing sequences of reactions known as nutrient cycles. Without the continuous cycling of these elements, all biochemical life processes would lead to a dead end.

Cyanobacteria are vital to two primary nutrient cycles in the ocean. In the carbon cycle, they photosynthetically “fix” carbon from air into organic matter at the base of the food chain, simultaneously releasing oxygen. Many are also important in the nitrogen cycle-a complex series of reactions and transformations, including one known as nitrogen fixation, which converts nitrogen from air and incorporates it into cellular compounds. The key is cyanobacteria’s ability to use molecular nitrogen (N2, or dinitrogen) as a source of nitrogen for their cells.

Cyanobacteria live anywhere there is light and moisture: in the open oceans, in pristine or polluted lakes and streams, in soils, hot and cold deserts, hot springs, brine pools, and salt ponds. In symbiotic relationships with algae and plants, they provide nitrogen to their hosts in exchange for a site to live on.

In many instances, cyanobacteria are visible to the naked eye. In coastal oceans, cyanobacteria form dark blue-green mats covering rocks and mollusk shells in tidal pools. Along upper limestone shores, they form black crusts that erode rocks.

In salt marshes throughout the world, several types of cyanobacteria play a key ecological role in binding sediments by forming dense layered mats. In the tropics, these mats, called stromatolites, become very thick; cyanobacteria inside them look almost indistinguishable from those in 3-billion-year-old fossil stromatolites. This is evidence that cyanobacteria inhabited the seas when the Earth was still young.

How oxygen got in the atmosphere
Three billion years ago, Earth’s atmosphere contained little oxygen. But ancestral cyanobacteria thriving in the early oxygen-free oceans evolved a biochemical mechanism for photosynthesis, which used light to generate cellular energy by splitting water molecules, and producing oxygen in the process.

For a billion years, growing and multiplying in the sea, they slowly raised the oxygen level in the atmosphere to 20 percent, the level that supports oxygen-breathing life. Cyanobacteria alone, directly or indirectly, are responsible for all of the oxygen in our air.

In every case, the green plants we are most familiar with, from unicellular algae to trees, owe their photosynthetic abilities to small chlorophyll-containing bodies within their cells known as chloroplasts-which look a lot like cyanobacteria. In fact, most microbiologists believe that chloroplasts are derived from cyanobacteria-or, more precisely, that ancestral cyanobacteria entered larger cells and became symbiotic in them, making them photosynthetic, and creating plants.

An ancient process
Both plants and cyanobacteria use carbon dioxide in air to synthesize cell carbon. But only bacteria can fix dinitrogen as a sole source of nitrogen in cells. Microbiologists believe this ancient process evolved very early, while Earth’s atmosphere was still without oxygen, because the necessary enzyme, nitrogenase, is inactivated by oxygen.

Cyanobacteria have mechanisms that allow oxygen-producing photosynthesis and dinitrogen fixation-two antagonistic physiological processes-to coexist in the same organism. In some, the two processes are separated by time: Photosynthesis happens during daylight and dinitrogen fixation at night. In more complex species, the two processes are separated by space, with dinitrogen fixation occurring only in specialized cells (heterocysts) within filaments.

Trichodesmium, a filamentous cyanobacterium, plays an important ecological role by replenishing nitrogen in the central oceanic gyres-areas of widely circulating currents in the middle of oceans-where nutrients like nitrogen, required by other marine microorganisms for growth, would otherwise be low. In calm weather, their buoyant red-colored colonies rise to the surface, resulting in massive blooms that can cover thousands of square kilometers. These blooms gave the Red Sea its name.

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The cyanobacterium Trichodesium erythraeum forms filaments (top) made up of many cylindrical cells, each about 9 micrometers (10-6 meters) wide. Hundreds of filaments form a raft-shaped colony of Trichodesium erythraeum several millimeters (10-4 meters) long (bottom). The raft is colored red because the cyanobacteria contain the red light-harvesting pigment, phycoerythrin. In calm weather, buoyant colonies rise to the surface in massive blooms that can cover thousands of square kilometers. These blooms gave the Red Sea its name. (Photos by John Waterbury, WHOI)

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In 1975, Ralph Lewin from Scripps Institution of Oceanography found something scientists never knew existed-Prochloron, a symbiotic cyanobacterium living in sea squirts in Palau. It was a legitimate “Eureka moment,” signifying the discovery of a previously unknown kind of organism known as prochlorophytes. But it also offered the tantalizing possibility of an even more momentous, heart-thumping discovery: how the first plant on Earth evolved.

Cyanobacteria inhabited the Earth billions of years ago, and scientists believe that ancestral cyanobacteria started symbiotic relationships with larger cells and provided them with the ability to photosynthesize. Eventually, these cyanobacteria evolved into chloroplasts, the photosynthetic factories inside all plant cells.

Prochlorophytes, like other cyanobacteria, contain chlorophyll a, a pigment important in photosynthesis. But unlike other cyanobacteria, which contain phycobiliproteins to absorb solar energy for photosynthesis, prochlorophytes contain chlorophyll b as their light-harvesting pigment.

So do all green plants.

Microbiologists speculated excitedly that prochlorophytes were on the same evolutionary pathway that led directly to chloroplasts in modern green plants.

But the theory didn’t hold. Phylogenetic studies showed that the three known prochlorophytes (Prochloron, Prochlorothrix, and Prochlorococcus) evolved separately from within the cyanobacteria, and none was on the same line of descent leading to higher-plant chloroplasts. Although chloroplasts also arose from cyanobacteria, their modern cyanobacterial relatives have yet to be found.

The study of cyanobacteria demonstrates the strength of scientific inquiry. Scientists follow paths that lead sometimes to unexpected discoveries and sometimes to nowhere. But every line of investigation adds to our knowledge.

Single-celled organisms are critical links in the ocean’s food web. Though ubiquitous and abundant, their microscopic sizes make them hard to sample and therefore hard to study. These protists, all found in Antarctic waters, are between 20 and 100 micrometers.

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A heliozoan is heterotrophic, meaning it consumes plant and animal matter including even small animals. (Dawn Moran, WHOI.)

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Diatoms (this one, Corethron) are at the base of the food chain, using photosynthesis to live, grow, and multiply. (Dawn Moran, WHOI.)

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THE INSIDE STORY-Richelia are cyanobacteria that live symbiotically inside single-celled marine plants called diatoms. The cyanobacteria have specialized dinitrogen-fixing cells that provide nitrogen to their hosts. Top: a light micrograph of the diatom Hemiaulus sp. Bottom: an epifluorescence light micrograph of the same cells, showing the red chloroplasts of the diatom and the orange fluorescence of the barbell-shaped endosymbiotic Richelia. (Photo by Dave Caron, Woods Hole Oceanographic Institution)

Squid ‘Sight’ – Not Just Through Eyes

In this case, the light organ is filled with luminous bacteria that emit light and provide the squid protection against predators. In turn, the squid provides housing and nourishment for the bacteria. 

BiologyNews.net. June 8, 2009  —  It’s hard to miss the huge eye of a squid. But now it appears that certain squids can detect light through an organ other than their eyes as well.

That’s what researchers at the University of Wisconsin-Madison report in the current issue (June 2) of the Proceedings of the National Academy of Sciences.

The study shows that the light-emitting organ some squids use to camouflage themselves to avoid being seen by predators – usually fish sitting on the ocean floor – also detects light.

The findings may lead to future studies that provide insight into the mechanisms of controlling and perceiving light.

“Evolution has a ‘toolkit’ and when it needs to do a particular job, such as see light, it uses the same toolkit again and again,” explains lead author Margaret McFall-Ngai, a professor of medical microbiology and immunology at the UW-Madison School of Medicine and Public Health (SMPH). “In this case, the light organ, which comes from different tissues than the eye during development, uses the same proteins as the eye to see light.”

In studying the squid for the past 20 years, McFall-Ngai and her colleagues have been drawn to the fact that the squid-light organ is a natural model of symbiosis – an interdependent relationship between two different species in which each benefits from the other.

In this case, the light organ is filled with luminous bacteria that emit light and provide the squid protection against predators. In turn, the squid provides housing and nourishment for the bacteria.

The UW-Madison researchers have been intrigued by the light organ’s “counterillumination” ability – this capacity to give off light to make squids as bright as the ocean surface above them, so that predators below can’t see them.

“Until now, scientists thought that illuminating tissues in the light organ functioned exclusively for the control of the intensity and direction of light output from the organ, with no role in light perception,” says McFall-Ngai. “Now we show that the E. scolopes squid has additional light-detecting tissue that is an integral component of the light organ.”

The researchers demonstrated that the squid light organ has the molecular machinery to respond to light cues. Molecular analysis showed that genes that produce key visual proteins are expressed in light-organ tissues, including genes similar to those that occur in the retina. They also showed that, as in the retina, these visual proteins respond to light, producing a physiological response.

“We found that the light organ in the squid is capable of sensing light as well as emitting and controlling the intensity of luminescence,” says co-author Nansi Jo Colley, SMPH professor of ophthalmology and visual sciences and of genetics.

Adds McFall-Ngai, “The tissues may perceive environmental light, providing the animal with a mechanism to compare this light with its own light emission.”

McFall-Ngai’s large research program into the relatively simple squid-light organ symbiosis aims to shed light on symbiosis affecting humans.

“We know that humans house trillions of bacteria associated with components of eight of their 10 organ systems,” she says. “These communities of bacteria are stable partners that make us healthy.”

Source : University of Wisconsin-Madison

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Bio plastics: Technicians at Genomatica prepare to make various
chemicals from sugar using bacteria.
Credit: Genomatica 

A startup uses strains of E. coli bacteria to convert sugar into valuable chemicals for textiles and other products.

MIT Technology Review, June 8, 2009, by Kevin Bullis  —  A company called Genomatica, based in San Diego, says that it can make the key ingredient in spandex from sugar, and do so at a cost that competes with current chemical processes, which use fossil fuels. It has developed genetically engineered E. coli bacteria that excrete a chemical called 1,4-butanediol, or BDO, which is used to make a number of products, including textiles, car parts, and pharmaceuticals.

The company announced that it has demonstrated a proprietary process that allows it to produce the BDO at greater than 99 percent purity, a technical milestone that clears the way for the one-ton-per-day demonstration plant that it plans to build next year. (Total worldwide production of BDO is about 1.5 million tons.) The company also reported increasing the productivity of the bacteria to a level that it says is near what’s needed to compete with petroleum and natural-gas-based processes.

Christophe Schilling, Genomatica’s CEO, says that its process will reduce energy use for making the chemical by about 30 percent. It will also decouple its cost from the cost of fossil fuels. He predicts that the company’s process will cost 25 percent less than conventional methods used to make BDO, provided the price of oil stays above $40 to $50 a barrel and the cost of sugar is about 10 to 12 cents a pound.

A number of companies are developing or have recently developed biological processes to compete with ones that rely on fossil fuels. John Pierce, the vice president for technology at DuPont’s applied-biosciences division, says that recent improvements in genetic engineering are helping researchers design organisms to make various chemical products. In the late 1970s, DuPont attempted to make BDO with organisms but never commercialized the process. The company has been more successful since then, opening a plant in 2006 that converts corn into 1,3-propanediol (PDO), which is used to make a fibrous plastic called Sorona.

Pierce predicts that the next 15 years will see a significant shift toward using biological processes to make chemical intermediates, as fossil fuels become more expensive. “Historically, petroleum has been cheaper [than sugar]–that’s why we’ve had a petroleum age,” he says. “It’s been the place everyone goes to get cheap raw materials. We’re in a period of transition now, where it’s becoming more and more frequent that it’s cheaper to do a biological process.”

Genomatica was founded in 2000 based on a set of computational tools used to predict how changes to metabolic pathways–series of reactions by which cells metabolize nutrients–could cause them to produce desired products, and to sort through the thousands of different pathways to find the best ones to try in experiments. Recently, the company has added the ability to produce organisms designed with this software, including tools for inserting and removing genes and selectively evolving the organisms to survive in high concentrations of the desired product. In addition to BDO, Genomatica is developing biological processes for making ten other chemicals, including the solvent MEK, which it says it can produce in idled corn ethanol plants.

The company will face difficult challenges as it moves toward a commercial-scale process for making BDO. Schilling says that the productivity of the organism still needs to be doubled. He expects that the increased productivity will be achievable, noting that the company has already improved the productivity of the bacteria by 20,000 times, having started with only trace amounts 18 months ago. But the last doubling of output could be difficult to achieve, as the organism’s output becomes increasingly optimized.

What’s more, moving from a lab scale to commercial scale can take years, and there’s no guarantee that it can be done without incurring deal-breaking costs. Some things that are easy to do in lab flasks, such as delivering oxygen to the organisms in a solution, are much more difficult in commercial-scale vats, Pierce says. It took DuPont 11 years to begin producing its biologically made PDO. And there are other practical considerations. Are the organisms vulnerable to viruses? If there’s a power outage, interrupting the flow of oxygen or nutrients, how fast can the organisms recover?

If it is able to scale up the production of BDO from the small amounts produced in a lab to the one-ton-per-day demonstration plant, the company plans to form partnerships with large chemical manufacturers, such as Dow Chemical, BASF, or DuPont, rather than attempting to build its own commercial plants, Schilling says.

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Mice that were engineered with a fat-burning pathway borrowed from bacteria (top mouse), remained thin, compared with normal mice (bottom) when both were fed a high-fat diet.  Credit: Jason Dean UCLA
Engineering mice with a fat-burning strategy from bacteria keeps the animals thin.

MIT Technology Review, June 8, 2009, by Courtney Humphries  —  Can burning excess fat be as easy as exhaling? That’s the finding of a provocative new study by researchers at the University of California, Los Angeles (UCLA), who transplanted a fat-burning pathway used by bacteria and plants into mice. The genetic alterations enabled the animals to convert fat into carbon dioxide and remain lean while eating the equivalent of a fast-food diet.

The feat, detailed in the current issue of Cell Metabolism introduces a new approach to combating the growing obesity problem in humans. Although the proof-of-concept study is far from being tested in humans, it may point to new strategies for borrowing biological functions from bacteria and other species to improve human health.

To create the fat-burning mice, the researchers focused on a metabolic strategy used by some bacteria and plants called the glyoxylate shunt. James Liao, a biomolecular-engineering professor at UCLA and a senior author of the study, says, “This pathway is essential for the cell to convert fat to sugar” and is used when sugar is not readily available or to convert the fat stored in plant seeds into usable energy. Liao also says that it’s not known why mammals lack this particular strategy, although it may be because our bodies are designed to store fat rather than burn it.

The glyoxylate shunt is composed of just two enzymes. The researchers first introduced genes for these enzymes from E. coli bacteria into cultured human cells and found that they increased the metabolism of fats in the cells. But surprisingly, rather than converting the fat into sugar as bacteria do, the cells burned the fat completely into carbon dioxide. The scientists analyzed gene expression in the cells and found that the new pathway promoted cellular responses that led the cells to metabolize fats rather than sugar.

The researchers then introduced the genes into the livers of mice. While normal mice gain weight when put on a high-fat diet, Liao says that the engineered mice “remained skinny despite the fact that they ate about the same and produced the same waste” and were as active as their normal counterparts. They also had lower fat levels in the liver and lower cholesterol levels. As in the cultured cells, the engineered mice did not convert the fat into sugar, which could have the dangerous side effect of promoting high blood sugar and diabetes. Instead, the scientists found a measured increase in their carbon dioxide output; the excess fat was literally released into thin air. The mice exhibited no visible side effects, although more detailed studies are necessary to verify that.

Liming Pei, a research associate at the Salk Institute for Biological Studies, who coauthored an editorial on the paper in Cell Metabolism, cautions that applying this specific approach to humans is many steps away. But the study is important in terms of finding new strategies to target obesity. Previous approaches, Pei says, “focused on stimulating existing natural pathways” for burning fat. The idea of introducing a strategy from another organism that is not present in the body is a novel one.

“This opens up an opportunity for understanding metabolism and finding new therapeutic applications,” Liao says. Someday, it may be possible to actually introduce these bacterial genes or proteins into humans, although Pei points out that such a feat poses many challenges, including a potential immune response to foreign genes. Another possibility would be to search for drugs that could mimic the effects of these enzymes. Furthermore, earlier studies reported glyoxylate shunt activity in chickens and rats, suggesting that higher organisms might retain the genes for this pathway but don’t use them; it might be possible to activate dormant genes.

Liao says that the study borrows strategies from synthetic biology, a field that has for the most part focused on engineering new functions into bacteria and other lower organisms. The study suggests that the same concepts could be applied to mammals: just as we create bacteria that produce biofuels, we could introduce new abilities into the bodies of humans and other animals.

“What I found fascinating is that it shows how you could use synthetic biology for human therapies in a highly novel way,” says James Collins, a synthetic biologist at Boston University. Current strategies for gene and protein therapy largely focus on single molecules–replacing a missing substance like insulin or inhibiting a harmful protein in cancer. Instead, Collins says, scientists might consider introducing an engineered pathway that allows the body to do something that it couldn’t before.

Learn How Bacteria Talk

Professor Bonnie Bassler discovered that bacteria “talk” to each other, using a chemical language that lets them coordinate defense and mount attacks. The find has stunning implications for medicine, industry — and our understanding of ourselves.

In 2002, bearing her microscope on a microbe that lives in the gut of fish, Bonnie Bassler isolated an elusive molecule called AI-2, and uncovered the mechanism behind mysterious behavior called quorum sensing — or bacterial communication. She showed that bacterial chatter is hardly exceptional or anomolous behavior, as was once thought — and in fact, most bacteria do it, and most do it all the time. (She calls the signaling molecules “bacterial Esperanto.”)

The discovery shows how cell populations use chemical powwows to stage attacks, evade immune systems and forge slimy defenses called biofilms. For that, she’s won a MacArthur “genius” grant — and is giving new hope to frustrated pharmacos seeking new weapons against drug-resistant superbugs.

Bassler teaches molecular biology at Princeton, where she continues her years-long study of V. harveyi, one such social microbe that is mainly responsible for glow-in-the-dark sushi. She also teaches aerobics at the YMCA.

“She’s really the one who’s shown that this is something that all these bacteria are doing all the time. And if we want to understand them, we have to understand quorum sensing.”

Ned Wingreen, Princeton, on Nova ScienceNOW

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Cell-to-Cell Communication in Bacteria
The research in my laboratory focuses on the molecular mechanisms that bacteria use for intercellular communication. Our goal is to understand how bacteria detect multiple environmental cues, and how the integration and processing of this information results in the precise regulation of gene expression.

The bacterial communication phenomenon that we study is called quorum sensing, which is a process that allows bacteria to communicate using secreted chemical signaling molecules called autoinducers. This process enables a population of bacteria to collectively regulate gene expression and, therefore, behavior. In quorum sensing, bacteria assess their population density by detecting the concentration of a particular autoinducer, which is correlated with cell density. This “census-taking” enables the group to express specific genes only at particular population densities. Quorum sensing is widespread; it occurs in numerous Gram-negative and Gram-positive bacteria. In general, processes controlled by quorum sensing are ones that are unproductive when undertaken by an individual bacterium but become effective when undertaken by the group. For example, quorum sensing controls bioluminescence, secretion of virulence factors, sporulation, and conjugation. Thus, quorum sensing is a mechanism that allows bacteria to function as multi-cellular organisms.

We have shown that the model luminous bacterium Vibrio harveyi and the related pathogen Vibrio cholerae each produce two different autoinducers, called AI-1 and AI-2, each of which is detected by its own sensor protein. Both sensors transduce information to a shared integrator protein to control the output, light emission in V. harveyi and virulence in V. cholerae. We have cloned the genes for signal production, detection and response in both species and have shown that the mechanism of signal relay is a phosphorylation/dephosphorylation cascade (see figure). Our recent studies combining genetics and bioinformatics (in collaboration with the Wingreen lab) show that the small RNA chaperone protein Hfq, together with multiple small regulatory RNAs (sRNAs), act at the center of these quorum sensing cascades. They function as an ultrasensitive regulatory switch that controls the critical transition into and out of quorum sensing mode.

V. harveyi and V. cholerae use the AI-1 quorum sensing circuit for intra-species communication and the AI-2 quorum sensing circuit for inter-species communication. To investigate the mechanism of AI-2 signaling, we constructed mutants and cloned the gene responsible for AI-2 production from several bacteria. The gene we identified in each case is highly homologous, and we named it luxS. We found that luxS homologues and AI-2 production are widespread in the bacterial world suggesting that communication via an AI-2 signal response system could be a common mechanism that bacteria employ for inter-species interaction in natural environments. We determined the biosynthetic pathway for AI-2 production as well as the AI-2 identity by solving the crystal structures of the V. harveyi and S. typhimurium sensor proteins in complex with their cognate AI-2 signals. The structural work was performed in collaboration with the Hughson lab. The V. harveyi AI-2 is a furanosylborate diester. Finding boron in the active molecule was surprising because boron, while widely available in nature has almost no known role in biology. The S. typhimurium crystal showed that its receptor binds a chemically distinct AI-2 that lacks borate. Importantly, the active signal molecules spontaneously inter-convert upon release from their respective receptors, revealing a surprising level of sophistication in the chemical lexicon used by bacteria for inter-species cell-cell communication.

Finally, we are focused on developing molecules that are structurally related to AI-2. Such molecules have potential use as anti-microbial drugs aimed at bacteria that use AI-2 quorum sensing to control virulence. Similarly, the biosynthetic enzymes involoved in AI-2 production and the AI-2 detection apparatuses are viewed as potential targets for novel anti-microbial drug design.

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On the microbial level, a person’s underarms are akin to lush rain forests brimming with diversity-and that’s a good thing-according to a new “topographic map” of human skin. 

NationalGeographic.com, June 2009, by Brian Handwerk  —  Long considered a source of odor and embarrassment, the humble armpit may be coming up in the world.

On the microbial level, a person’s underarms are akin to lush rain forests brimming with diversity-and that’s a good thing-according to a new “topographic map” of human skin.

 

Most of our skin is like an arid desert, said study co-author Julia Segre, of the National Human Genome Research Institute in Bethesda, Maryland.

“But as you walk through this desert you encounter an oasis, which is the inside of your nose,” she said. “You encounter a stream, which is a moist crease. [These] areas are like habitats rich in diversity.”

And like the “friendly” bugs in the human digestive system, these native bacteria of the epidermis promote skin health and could even help scientists find new ways to treat skin diseases.

(Related: “Beach Bacteria Warning: That Sand May Be Contaminated.”)

Well Adapted

The study, published this week in the journal Science, has revealed that human skin hosts a much more diverse set of bacteria than previously thought.

Samples of skin bacteria grown in the lab had suggested that a single genus, Staphylococcus, was dominant on human skin.

But by looking at the microbes’ genes, Segre’s team found at least 18 different phyla of bacteria dwelling in 20 different skin habitats. (In biology, a phylum is a group of animals that are similar enough that they likely share a common origin.)

What’s more, these microbes are adapted to their habitats rather than to individual humans, Segre said.

“The bacteria in my underarm are more similar to those in your underarm than they are to those on my forearm,” she said.

The map presents a new way of looking at various skin conditions, the study authors note.

For example, researchers could compare the map of the body’s “normal” bacteria with one accompanying a wound or a disease such as eczema. This could reveal how these ailments-and our treatments of them-act on good and bad skin bacteria.

No Cause for Alarm

Germophobes needn’t freak out. Serge stresses that many of the microbes are “healthy bacteria” that keep our largest organ in good condition.

For example, germs that live in naturally oily regions, such as the outside of the nose, feed on the skin’s lipids and produce natural moisturizers to prevent skin from becoming chapped.

“People are eating probiotic yogurts to promote [beneficial] bacteria growth in the gut, but we want to sterilize the skin,” Serge noted.

“We should think about proper sanitation with the skin, but not sterilization. There are good bacteria that really promote healthy skin.”