Biology: critters that should not exist!

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Critters, critters, everywhere!

Astronomers have just discovered two Earth-size, rocky planets around a nearby star. Though the planets are way too broilsome for life, they suggest that steady improvements in telescope technology has made the discovery of habitable planets just a matter of time.

But as astrobiologists continue to search for life in space, geo-biologists (ok, we coined that) continue to find bizarre life in strange places on Earth: in the dark ocean depths, between grains of sand, and at roasty-toasty temperatures once considered deadly.


Illustration of brown planet mottled with red in space and sun-like star in the distance

Illustration: NASA/Ames/JPL-Caltech
An artist’s rendition of one of the rocky planets just discovered by the Kepler mission. It’s just a bit smaller than Earth — and a lot hotter, but it still raises questions about the different forms that life could take in space — and on Earth.

Hot, humid, and totally alive!

Fifty years ago, nobody believed organisms could survive near the boiling point of water. When Thomas Brock started probing the hot springs in Yellowstone in the 1960s, he was not looking to overthrow a ground rule of biology. Instead, the University of Wisconsin-Madison professor, then at Indiana University, sought to study bacteria in a simplified, real-world environment.


Smoldering pool of bright blue water is surrounded by halo of dark orange. Land surrounding pool is purple

An aerial view of Grand Prismatic Spring in Yellowstone National Park. Steam rises from hot, sterile water surrounded by mats of brilliant orange algae and bacteria. Yellowstone’s hot springs and boiling mud pots have been a world headquarters for the discovery of thermophilic (heat-loving) microbes. The spring is approximately 75 by 91 meters.

At the time, and even today, precious little was known about how bacteria live their lives — unless they cause disease.

As Brock sampled his way up a hot stream, he approached its source in a hot spring, and the water temperature rose steadily.


Flat dark orange mass is textured like a sponge

Thermophilic bacteria at Mickey Hot Springs, Oregon, gather minerals that eventually turn into solid rock.

At the time, biologists thought life would not tolerate temperatures near 80° C. But Brock kept finding bacteria, so he kept looking. Eventually, he found some that could live and reproduce near the temperature of boiling water — 100° C.

The prize of his collection was a bacterium he named Thermus aquaticus (for its hot-water habitat) and placed in a public repository for study by other scientists.

How does PCR work?

Over the years, T. aquaticus proved interesting indeed. For one thing, it was the first of more than 50 species of thermophilic bacteria known to tolerate or require temperatures near water’s boiling point.

For another, it was the first of the Archaea (ancient ones), primitive microorganisms that scientists now regard as a separate and highly primitive kingdom of life.

Deep roots indeed

Because thermophiles are Archaeans, and prefer the steamy conditions typical of early Earth, many scientists think they may tell us about the origin of life itself.

To any basic scientist, those contributions would be enough. But because their enzymes work in high temperatures, where chemical reactions are faster, the thermophiles have proven to be extraordinarily useful.

Today, enzymes derived from thermophiles are used to convert millions of pounds of corn (maize) into sugar to sweeten soft drinks.

But more important, at least to scientists who don’t guzzle fizzy pop at the lab bench, T. aquaticus supplied TAQ polymerase, the essential enzyme for polymerase chain reaction, AKA PCR.

PCR is an artificial technique that does what living critters do every day — replicate DNA. But PCR is the rocket ship of replication, since it allows you to multiply a piece of DNA a billion times in a few hours. That produces enough DNA to analyze to your heart’s content — for genetic engineering, biotechnology and forensic purposes.

PCR depends on TAQ polymerase.

Aware that PCR and soda pop are both billion-dollar industries, corporations and scientists around the world have frantically searched for other thermophiles that may have equally useful enzymes. They’re looking in odd places — not just hot springs and volcanoes, but also deep-sea vents, hot petroleum-bearing rock, the outflow of geothermal power plants, and smoldering piles of garbage.


Two tiny squid crawl on ocean floor. One squid is orange with florescent spots, the other is smaller, white and also has spots

Two bobtail squid showing their signature bacterial glow, and the animal’s ability to change color.

Prowling for glow-in-the-dark squid

Call me Bob.

Short for bobtail squid. (Did I mention that I’m a 3-4 centimeter cephalopod, formally Euprymna Scolopes?)

Anyway, I hang out in shallow waters around Hawaii. Save your crocodile tears — somebody’s got to live in the sunny, tropical ocean. Anyway, here’s my problem: Even though I have 10 tentacles, I don’t have spines, poisons, or any other decent defense.

So I spend my days burrowed in sand at the ocean bottom, trying to keep out of mischief. Still, a fellow’s got to eat, don’tcha know, so I cruise at night, looking to grab a bite.

Here’s the snag: All sorts of nocturnal predators seem to have this thing about calamari sushi.

Light before flashlights

A long time ago, my ancestors evolved a nifty defense against their big teeth: stealth. Even their tiny squid brains figured out that predators could see them from below, as tasty dark blobs against the bright ocean surface.

Since this was before flashlights, my relatives had to improvise. So they press-ganged billions of luminescent bacteria into making light for them. The idea was to make us just as bright as the ocean surface — and hence invisible.

At least, this is how my great-aunt Tentacla tells it. To tell the truth, I think it had more to do with the evolutionary advantage of being hard to see.

Anyway, my ancestors fed the bacteria, and gave them a home in two specialized light-emitting organs. These “photophores” have a reflective membrane to shine all their light down, toward the hungry predators. They use a diaphragm to control brightness, and even have a lens to spread the light.


Blue arm-like appendage is attached to a green organ with three egg shaped holes in it

Courtesy Margaret McFall-Ngai, University of Wisconsin-Madison; confocal microscopy by S. Nyholm.
The flashlight squid uses this blue-stained arm to “sweep” bacteria from the water into three intake holes (arrows). Green and blue stains were used to make this confocal microscope image of a cross-section of the squid’s bacteria-harvesting apparatus.

The photophore reminds me of a backwards eye — one that makes light rather than detects it.

My folks even figured out how to switch the bacteria “on” when needed.

In return, the bacteria got room and board, in the biological deal they call “symbiosis” or “mutualism.” Sometimes I think people could learn from this cooperative spirit….

But that’s enough thinking for today. My squid brain is squashed.

As I burrow into the sand for another daytime nap, permit me to introduce somebody who considers me almost as fascinating as I do.

Seriously speaking…

Margaret McFall-Ngai, a biologist at University of Wisconsin-Madison, says the bobtail squid may pretend it’s cooperating in a symbiosis with those light-making bacteria, but the reality is more ominous.

She says there’s evidence that this may be slavery, not symbiosis, since the squid, “inhibits the growth of the bacteria to enhance their luminescence.” The bacteria, Vibrio fischeri, could make a better living drifting in the ocean, or in the gut of another marine animal, McFall-Ngai observes.

The concept of bacterial enslavement broadens our perspective on the many possible relationships in the living world.

Most people, if they think about bacteria at all, conjure up disease and decay, but people would be dead without bacteria, since the little critters play essential roles in producing vitamins and preventing disease.

Since the bacteria in our guts vastly outnumber the cells in our bodies, it helps that they’re helpful!

Nevertheless, and for understandable reasons, bacteriologists have traditionally focused on disease-causing organisms, and, for simplicity, on one species at a time. But that skews our view of how bacteria actually live, says McFall-Ngai.

Three cheers for complexity!

Complexity and subtlety may be the hallmarks of these interactions, and the complexity begins by recognizing that V. fischeri is closely related to V. cholerae, which causes the human intestinal disease, cholera.

Cholera is caused by a V. cholera toxin similar to a toxin produced by the light-emitting bacterium. But far from harming the poor little bobtail, that toxin signals it to secrete food for V. fischeri, so the toxin is really a chemical “dinner bell.”

And this raises the intriguing notion that a cholera bug secretes toxins not to kill its host but to discuss its menu. If so, our whole notion of pathogenesis may need rewriting, McFall-Ngai suggests. “Maybe when we’ve been studying cholera pathogenesis we’ve been studying an aspect of a normal conversation that’s gone wrong.”

Indeed, the traditional bacteriological view of bacteria as pathogens to be studied in pure culture may be “like trying to understand the complexity of all the cultures that lived in Paris by studying the activity of the Nazi occupiers,” McFall-Ngai suggests. “You are studying groups that don’t belong there, and have disrupted the normal activities.”

Want more on how the flashlight squid bullies its bacterial brethren?

Both images courtesy M. Antonio Todaro
Meet the meiofauna. The first little guy is from the subgenus Chaetonotus. Rollover to meet Heteroxenotrichula squamosa.

Between the grains

(1996 story, only photos have been updated)

To zoologist Robert Higgins, small is beautiful. His infatuation with small creatures — “meiofauna” — dates to a student job in a biology lab that paid 35 cents an hour. Instead of quitting for more lucrative work, Higgins was intrigued.

He’d heard about tiny, amazingly diverse creatures, and put grains of sand and muck through a fine mesh, and used a microscope to find hundreds of organisms.

Forty-four years later, Higgins has retired from the Smithsonian Institution, but he’s still goggling at meiofauna — a complex group of animals found in most Earthly environments.

Indeed, a handful of wet sand could contain more biological diversity than a whole rain forest, Higgins says.

In the course of peering through countless microscopes, Higgins has discovered hundreds of species. With Danish biologist Reinhardt Kristensen, he found an entire phylum, called Loricifera.

Phyla are the broadest categories of organisms, based on structure, and according to the International Association of Meiobenthologists, “The majority of recognized phyla have meiofaunal representatives. Currently, 20 phyla considered to be meiofaunal from the 34 recognized phyla of the Kingdom Animalia. Out of these 20 phyla, five are exclusively meiofaunal in size.”

Active phase resembles a slug; during anhydrobiosis, it shrinks to a ball about half as large.

Photo: Giulio Melone, department of biology, Milan University.
A bdelloid (a type of meiofauna) shrinks when it undergoes anhydrobiosis. The dormant, dehydrated bdelloid has greater resistance to environmental stress but is ready to spring back to the active form in conducive conditions.

Meiofauna living between grains of sand have made some fancy adaptations to their harsh environment. Some have hooks on their feet, used to grab the sand. Others have hooked mouthparts, also useful for locomotion.

Beyond freeze-dried

To survive a difficult environment, meiofauna called tartigrades have evolved an amazing adaptation called “anhydrobiosis.” In this form of suspended animation, the animals replace water in their cell membranes with sugar, protecting the membrane from destruction through radiation and freezing. Microorganisms die when their cell membrane ruptures.

During anhydrobiosis, organisms are rather like plant seeds or bacterial spores, Higgins explains. “They can dry up for 100 years, and be rewetted, and come right back to active metabolism.”

Fun is fun. But what is the practical importance of studying stuff that can hardly be seen, doesn’t seem to cause disease, and is — at least to some — utterly ugly?

In other word, who cares about microscopic beach crud?


Toddler boy in summer outfit and sun hat squats on sand, holding sand toys and peering into a bucket

Photo: Chris. P
Has this young scientist found some miraculous meiofauna in the blue bucket?

Meet the beach-cleaning crew

Anybody who likes to hang on the sand should be interested, Higgins says. “This is the system that helps keep our beaches clean.” Plankton, bacteria, all sorts of dead material is continually washing ashore, and a lot of people love to sit on beaches.

There’s a public-health angle here. Hookworms occur on beaches where dogs defecate, but meiofauna may consume hookworms, along with other nematodes. “So if we upset that, we could upset beach cleanliness,” Higgins says.

Higgins notes that meiofauna comprise a basic part of the food web, and disturbing them could have unforeseen consequences for the entire system.

Still, it’s hard to escape the notion that most of the motivation here is the pure scientific urge to discover, to classify, to understand. Meiofauna, Higgins notes, were seen under the microscope Anton van Leeuwenhoek invented in 1683.

The key to finding these things, Higgins indicates, in patience, technology, curiosity — and institutional support. “If you stare through a microscope for hour after hour, you have a chance of finding these things, but if you need to get out a certain number of papers each year, you have to take shortcuts and you won’t find as much.”


Mound of sand, covered in white and pink worms, emits three plumes of black water. Two canisters hold instruments.

At mid-oceanic ridges, scientists have found “black smokers” — vents for geologically heated, chemical-rich groundwater. The weird organisms at these ridges may thrive in super-hot conditions or live independently of sunlight and photosynthesis. Mid-oceanic ridges even have been the site of the first life.

Fantastic freak show

Biology has lots of other oddities:

bullet_archea A shrimplike native to Panama’s Pacific beaches transports itself by rolling. When the animal washes ashore, it arcs its body into a ring and rolls back into the water, pushed by the head and tail at the stately pace of 3.5 centimeters per second. Nannosquilla decernspinosa may have learned to spin in its cramped burrows, but it’s the only known rolly-roller in the animal kingdom.

bullet_archea Sponges, considered the first multicellular organisms, were always thought to be dumb, simple filter-feeders that strain their dinner from sea water. But now it appears that some sponges in the phylum Cladorhizidae, living in the Mediterranean, are willing to reach out and touch their prey. The sponge has filaments that capture plankton and reel them in for digestion.

bullet_archea Bacteria can live deep underground, and in 2006 a team found bacteria 3 kilometers below South Africa, in a niche that had been isolated from the surface for several million years. The discovery demonstrates the resilience of life on Earth and hints that life could exist deep inside Mars.

bullet_archea A large number of ancient bacterial relatives — Archaea — live in the Antarctic. These critters are a large part of the food web in a cold, remote place whose ocean is a major source of protein in our diet.

— David J. Tenenbaum


Terry Devitt, editor; S.V. Medaris, designer/illustrator; Jenny Seifert, project assistant; David J. Tenenbaum, feature writer; Amy Toburen, content development executive


  1. Thermophiles like it hot.
  2. Thermophiles in Yellowstone.
  3. More about squid-vibrio symbiosis.
  4. More about Vibrio fishereri.
  5. Life in the vents multimedia.
  6. Meiofauna picture gallery.
  7. More meiofauna resources.
  8. Make your own PCR reaction.
  9. Video: watch a water bear go into anhydrobiosis.
  10. Anhydrobiosis and radiation resistance.
  11. Meiofauna classroom activity.
  12. More strange biology.