Ask an Expert: When Life Gets Extreme'
They're known as "extremophiles" -- rugged life forms that thrive under the most extreme conditions. They cling to life at the edge of lava. They thrive under thousand-years-old layers of ice. They withstand radiation bombardment and still reproduce. They bathe in acid and keep on going. The can be dried, dehydrated and desiccated, yet still go about their business. (And you thought your days were challenging!)
On Thursday, July 8, NASA scientist Richard Hoover from NASA's Marshall Space Flight Center answered your questions about extremophiles and the hunt to find them in some out-of-the-way corners of Earth -- including Antarctica.
More About Chat Expert Richard Hoover
Dr. Richard Hoover, a Marshall employee since 1968, is the Astrobiology group leader at NASA’s Marshall Space Flight Center in Huntsville, AL. Hoover is recognized for his work in X-ray and extreme ultraviolet light optics – ranging from microscopes to telescopes. His full-disk images of the sun in the x-ray and ultraviolet wavelengths are among his many innovative advances for the field of Astrobiology.
Hoover has collected meteorites and microbial extremophiles from Antarctica; novel bacteria from Glaciers and permafrost of Antarctica, Patagonia, Siberia and Alaska and from haloalkaline lakes, geysers, and volcanoes of California, Alaska, Crete and Hawaii. He has discovered three new species of bacteria from Mono Lake in California – Spirochaeta Americana, Desulfonatronum thiodismutans and Tindallia californiensis -- and another, Carnobacterium pleistocenium, which survived for 32,000 years in a frozen Alaskan pond.
He holds 11 U.S. patents and in 1992 was named NASA's Inventor of the Year. He served on editorial boards of several scientific journals and the boards of directors of the American Association of Engineering Societies, and the Council of Scientific Society Presidents. He is the author or editor of 33 books and some 250 papers on astrobiology, extremophiles, diatoms, solar physics, X-ray/EUV optics and meteorites. He co-directed the NATO Advanced Study Institute on Astrobiology in Crete, for which he published the book "Perspectives in Astrobiology" in 2005.
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abishekn: Sir, good evening. What are extremophiles? Are they aliens?
Richard: When we talk about extremophiles, we're talking about life forms that inhabit what human beings consider "hostile" environments. Such environments are extremely cold, such as glaciers and icecaps, or extremely hot, such as deep sea hydrothermal vents, volcanic fumaroles, and geysers. Other extreme environments include places such as salt flats, highly alkaline pools of water, or acidic pools, and places where there is very high radiation levels, such as spent fuel rods from nuclear reactors. Another group of extremophiles are those that must live in total absence of oxygen -- these are called anaerobes. Even though we consider them "extremophiles," if these organisms could talk, many of them would probably consider humans as extremophiles because they aren't killed by all this "toxic" oxygen that we breathe every instant!
abishekn: Do aliens exist on Titan?
Richard: We really don't know if there's any life on Titan. This wonderful moon of Saturn is extremely cold, but there's evidence of water ice on Titan, and perhaps even liquid water near the core. The reason that's important is because all life that we know of has an absolute requirement for water.
abishekn: Sir, do aliens exist on Mars?
Richard: Mars is a much more likely habitat for life than Titan. We have extremely strong evidence that large bodies of liquid water existed on Mars in the past, and it's well-known that the polar ice caps of Mars contain huge amounts of frozen water today. In the winter time, the north polar ice cap of Mars gets covered over by a thick layer of frozen carbon dioxide, which we call dry ice. But in the summertime, that carbon dioxide layer goes back into the atmosphere and leaves behind the frozen water ice cap. We also have very strong evidence that just beneath the surface of most of the planet, there's a layer of permafrost which is composed of water frozen along with grains of soil. We also know that in regions that aren't at the poles, the temperatures of the surface of Mars during the summertime when the sun is shining brightly on the planet can go well above 0 degrees C (32 F). This clearly means that water films between the soil grains in the permafrost could seasonally melt and provide suitable habitats for many types of bacteria that we know inhabit similar regions on our own planet. So it's not impossible that there may well be microbial life on Mars today.
Ediz_Celik: Is there any species that not be effected by radiation? Sorry for my English :)
Richard: All species of life that we know of are sensitive in some degree to different levels of radiation. Some organisms are incredibly insensitive -- by that I mean they can survive enormously high doses of radiation. One organism that's extremely insensitive to gamma and X-ray radiation is Deinococcus radiodurans
. But even that organism can be killed by radiation.
abishekn: Sir, how do you get the aliens' picture?
Richard: The tardigras image on the story is not one that I made, but it was clearly made with a scanning electron microscope. I use the scanning electron microscope extensively to study living and fossil microorganisms because it allows you to take extremely high magnification pictures with a great depth of field. It can actually be used with magnifications in excess of 100,000X.
abishekn: What is the smallest animal in our solar system?
Richard: I don't immediately know the smallest animal in our solar system, but the smallest animals on Earth are within the group of life forms that we call protozoans, which are single-celled animals. These are within the broad group known as eukaryotes, and the smallest eukaryote is considerably larger than the smallest bacterium. There are bacteria which are called "dwarf" bacteria or "ultramicro" bacteria that are about 50 nanometers in diameter. These are the smallest prokaryotes that we know -- still larger than the smallest viruses known.
Ediz_Celik: Which planets or moons are possible to have an extreme life in our solar system?
Richard: Astrobiologists are always trying to determine the best locations in our solar system that might be suitable abodes for life. The primary criteria is the existence of water. One of the top locations, of course, is the planet Mars. We know there's water on Mars today, both at the polar ice caps and in the permafrost just beneath the surface. Other places which are considered prime candidates for life include Jupiter's ice moons, such as Europa and Ganymede, and the wonderful ice moon of Saturn called Enceladus. Other interesting places in our solar system where we know there is water are comets.
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Fred: Would an extreme life form be able to survive in a black hole?
Richard: I would be totally astonished if any form of life were capable of surviving inside a black hole. We know that black holes have incredibly high gravitational fields and that radiation can't escape a black hole. In the same way, it's inconceivable that life as we know it could survive in the interior of any star. The reason for that is that life as we know it requires a complex set of organic macromolecules, and these substances -- such as amino acids, proteins, carbohydrates, DNA, RNA, and enzymes -- would all be destroyed at temperatures such as those encountered at the surface or interior of stars.
JJ_Jordan10: How do these creatures survive under these extreme conditions?
Richard: The microorganisms that we call extremophiles have evolved an incredible array of mechanisms for survival under these extreme conditions. For example, the microorganisms that live on and in the ice of the polar regions of our planet have specialized "cold shock" and "antifreeze" proteins that allow the fluids within the cells to remain in fluid state well below the freezing point of water. They also have substances that prevent the formation of ice crystals that rupture the cells and therefore kill them, even when the temperature goes so low that they DO freeze. There are organisms that live in high salt environments that have membranes and mechanisms that protect them from the osmotic pressure between the liquid water the high salt environment on the outside. The organisms that survive high radiation environments, such as some of the cyanobacteria in Antarctica, have thick sheaths of polysaccharides that become black when baked in the sun and form natural sunscreens to protect the organism from visible and ultraviolet radiation. Organisms like Deinoccocus radiodurans
have the ability to rapidly repair DNA damage caused by radiation hits. When they get zapped, they just fix the problem and go right on. This is part of the amazing ability that a wide variety of life forms have developed so that they can inhabit virtually every niche on our planet.
abishekn: Sir what type of creatures live in place of volcanic eruptions?
Richard: We don't know of any organisms that could actually live in a volcanic eruption, as the temperatures would go so high that the organic matter would be cremated. However, an enormous number of life forms inhabit the regions around volcanoes at the sea floor. These are the deep sea hydrothermal vents that are home to enormous numbers of sulfur bacteria that serve as the primary foodstuff for the two worms, shrimp -- they are, in effect, the base of the food chain around the vents. These bacteria don't get their carbon or energy from eating food or using light for photosynthesis, but rather from chemical reactions with carbon dioxide, hydrogen sulfide, methane, and other chemicals and minerals available at the vent site.
longsheryl: Have you seen any extremophiles on any other planets?
Richard: I haven't seen any extremophiles on other planets. :) However, during the Viking mission, one of the experiments called the Labeled-Release Experiment obtained data that was consistent with biology. This was a controversial finding and a lot of the scientific community was convinced that the results were caused by chemical rather than biological processes. one of the major arguments that was given was that there was no water on Mars, and if there was no water, there could be no life. We now know that just beneath the surface in the permafrost, there's a layer of frozen water that would melt as soon as the samples were introduced into the experiment on the spacecraft. So it's possible that we may have actually already obtained data on life on Mars. However, in order to answer that question for sure, it would be most valuable to send an experiment to Mars to conduct further searches for evidence of present-day life on the Red Planet. The study of extremophiles carried out during the last 30 years has revealed to the scientific community that there's nothing we know about Mars today that tells us it would be impossible for many Earth organisms to live there. So if extremophiles from Earth could conceivably live in conditions such as we know exist on Mars, we certainly can't rule out the possibility that there's life on Mars today, or that there was life on Mars when it was much warmer and wetter than it is at the present time.
KLJStats: Read just a little very recently about extremophiles living in hot water vents in the ocean, but not black smokers. Can you talk to those briefly?
Richard: Microbial extremophiles do, in fact, inhabit the black smokers. All region of the oceans that have been studied have been found to contain life. However, from the hydrothermal vents, there are plumes of water that initially escape with temperatures as high as 400 degrees C -- and it's highly unlikely that any life forms would be capable of surviving such high temps. However, these vents are surrounded by enormous quantities of ocean water that is typically 2 degrees C at the deep sea floor. So you don't have to venture far from the direct plume in order to reach temperatures that are perfectly suitable for the microorganisms we call hyperthermophiles, which can live at temperatures above 120 degrees C.
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Anom: What benefits arise from studying these? What have we learned about surviving in space?
Richard: The benefits of studying microbial extremophiles can be phenomenal! It wasn't too long ago that a study of a geyser in Yellowstone National Park was found to contain living organisms growing at a temperature of 80 degrees C by Professor Brock. At that time, the scientific community knew that DNA molecules become denatured -- the double helix comes apart -- and hence everyone thought this result had to be wrong. It was later found that this tiny organism had a special enzyme that allowed the DNA to remain together at such a high temperature. In fact, it was discovered that this enzyme allowed ANY DNA to remain together at a high temperature. The organism was named Thermus aquaticus
for "hot water" and the enzyme was called "taq polymerase." The taq polymerase enzyme made it possible to rapidly amplify any piece of DNA by a process called cycling, and this ultimately opened up the entire modern field of DNA analysis. The enzyme is sold all over the world today for a market of hundreds of millions of dollars, and this technique ultimately made it possible to perform genetic engineering and decode the entire human genome. Profound advances in science and microbiology came about from the discovery of a wonderful little extremophile at Yellowstone!
Spacesidehouses: How would you classify an unknown species, which you may find in your 'expedition' of sorts?
Richard: When a sample is returned, the study begins by the formation of enrichment cultures. My colleague, Dr. Elena Pikuta, introduces the sample into different types of growth media under anaerobic conditions (because our primary area of research is on anaerobic extremophiles). After a period of time, which can vary from days to years, the organisms begin to grow. Then she goes through a very elaborate process of isolating the different strains that are growing in each medium. By using classical techniques, such as microscopic observation, it's possible to tell whether the organisms belong to broad groups such as vibrions, cocci, bacilli, spirochetes, etc. and whether they react to the Gram stain as having Gram-positive or Gram-negative cell walls. After she has achieved pure cultures, she then details characterizations of the properties of the organisms: temperature of optimum growth and temperature range; Ph-optimum and Ph-range; salinity-optimum and salinity-range, etc. Once these are determined, the DNA is separated for 16S RNA gene sequence analysis. This allows one to determine the position of the organism by systematic taxonomic methods and to know whether it's a new species, new genus, or belongs to a previously described species. If it's new to science, then the organism is deposited in two separate international collections -- ATCC; DSMZ; Institute Pasteur; etc. -- and then formally described and published. If it is published in a journal such as the International Journal of Systematic and Evolutionary Microbiology (IJSEM), it's then recognized the world-over as a valid new species or genus of life. If it's published in some other journal, it must be submitted to IJSEM and if approved, it becomes valid.
01cj(: How do these creatures survive swimming in acid?
Richard: The microorganisms known as acidophiles LOVE acidic conditions. In fact, we discovered a microorganism from Chena Hot Springs in Alaska that was introduced into a medium at with a Ph of 4 (mildly acidic). After it grew there for about two weeks, I was examining it when a tiny drop of the liquid landed on my hand while I was putting the slide on the microscope. When I started to focus, it felt like there was a wasp on my hand! I looked down and saw this tiny drop had already made a white spot and was burning fiercely. I immediately stopped looking into the microscope, washed my hand, and asked Dr. Pikuta what the Ph was? She said, "Four." I said, "I think we better check." We tested immediately, and the Ph was 1.5, which is like acid from a car battery, rather than a lemon. So this organism wasn't happy in Ph 4 and simply produced lots of acid to make its home more hospitable to it -- but it wasn't very hospitable to my hand!
michael: Sir, have extremophiles done some new significant changes in our environment?
Richard: About 2.7 billion years ago, cyanobacteria started growing in enormous numbers in the oceans. Prior to that time, the Earth's atmosphere contained large amounts of carbon dioxide, and very little oxygen. It would have been entirely impossible for oxygen-breathing animals to live on Earth in that atmosphere. But the cyanobacteria were producing oxygen by photosynthesis and consuming carbon dioxide, and they totally changed the atmosphere of our planet. This change made it possible for all of the great animals of the land to come into existence. If not for these changes produced primarily by the cyanobacteria, human beings would not live on the planet Earth today.
YM: The moss you're shown holding in the photo above, is that the oldest example of an organism that has been dormant in ice?
Richard: The moss was about 30,000 years old, and we described a new species called Carnobacterium pleistocenium that had been frozen in the ice of the Fox Tunnel in Alaska for 32,000 years. As soon as the ice melted, the organism came out of the ice and began to swim. There are other organisms that have been recovered from even more ancient ice, some as old as 8 million years. There are also reports of organisms recovered from salt crystals many tens of millions of years old. The important point is that under certain conditions, microorganisms can remain alive for very long periods of time. This means it's not impossible that Earth microorganisms may have been thrown off our planet when great impacts of asteroids hit the Earth, such as what possibly caused the extinction of the dinosaurs. In this way, we may have transferred Earth life to other bodies of the solar system. Likewise, big impacts on Mars have sent rocks from Mars to the planet Earth, so if there was life on Mars in the past, it's not impossible that some of it might have been sent to Earth by these kinds of huge impacts.
abishekn: What is the least temperature were a organism survive?
Richard: Microorganisms have the ability to survive extreme cold. We routinely keep living microorganisms stored in our freezer at -80 C. There's no reason to believe that very much lower temperatures would kill these organisms. Microorganisms are usually much more sensitive to high temps. The organisms called psycrophiles absolutely require low temperatures for growth and die when the temperatures go above 15 degrees C.
Ryan_Robinson: Obviously without going into too much detail, but if extremophiles were to exist that were extraterrestrial in origin, do you have any vague guesses into how different their biology may be? Ie: Other potential genetic codes apart from DNA? Are the raw material found say on Mars similar enough to Earth that similar proteins could be made?
Richard: Excellent question! We've given a lot of thought to what alien life forms might look like. One hypothesis is that they'd be very much different from Earth life. Of course, the other hypothesis is that they'd be very similar or perhaps even identical to Earth life. The fascinating thing about life on Earth is the phenomenal uniformity of all living things from the smallest bacterium to the cells of the human brain. They all are made using the same critical set of biogenic elements, primarily carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Furthermore, they all are made with proteins using exactly the same set of 20 genetically encoded life-critical amino acids. Furthermore, amino acids can come in two mirror-image forms (except for glycine, which is symmetric). These two forms are left-handed or levorotary (L-) and dextrorotary, or right-handed (D-). This is the phenomena of chirality. When amino acids are made by abiotic processes, you get equal quantities of D- and L-. However, the proteins in living organisms are made entirely of L-amino acids. This is called homochirality, and it was thought by Pasteur that it represented the secret of life. Furthermore, all of the ribose sugars in RNA and deoxyribose sugars in DNA are entirely right-handed (D-). This is crucial because if you introduce the wrong sugar, you'd destroy the right-handed helix of the DNA molecule -- and if you introduced the wrong amino acid, these phenomenally complex proteins or enzymes wouldn't fold properly and would be unable to work. There's no reason that you couldn't have life that utilized exactly the opposite kind of amino acids and sugars, as long as all the amino acids in its proteins were D-aminos and all of the sugars were L-sugars. This type of life could conceivably exist, but we've never found it on Earth. That doesn’t mean it doesn’t exist, and we’ve started looking by growing microorganisms in what we call alternate chirality substrates. To our great astonishment, we discovered that several of our new species of bacteria were able to eat and grow on these bizarre foods. However, there is no evidence that they use the alternate chirality material in either their DNA or in their proteins. What they appear to be doing is just taking this strange food and using special enzymes or metabolic pathways to change the D-amino acids into L-amino acids which is what they like. However, if we ever did find organisms that grew using the "wrong" kind of sugars or amino acids for life-critical biomolecules, it would be an astonishing discovery of representatives of life forms that Paul Davies would consider to represent the "shadow biosphere."
(Moderator Jason): We've got time for just a few more questions...
Ryan_Robinson: I've heard of certain mites being able to survive the vacuum of space. That is more of a question of hardiness though. What would be interesting is to know is if any organisms such as bacteria have been seen to adapt to the low gravity environment of the ISS, or indeed maybe even the vacuum of space?
Richard: It's absolutely true that microorganisms can survive in the hard vacuum of space. One of the ways that we keep pure cultures alive for long periods of time is by a process called lyophilization, which is freeze-drying. The organism is frozen to liquid nitrogen temperatures and put in a hard vacuum -- to revive it, you'd essentially just add water. This is done all over the world, and it's amazing that all microorganisms -- even, for example, cells of mammals -- are capable of surviving this process. It may suggest that they adapted to these conditions in deep space in the first place, since there was nowhere on the planet Earth where a vacuum existed prior to the invention by Toricelli. Also, microorganisms were collected by the Europeans from the exterior of spacecraft, and they were found to be in living state.
RyanD86: Query: In the past few years, rovers and orbiting probes, above or on Mars, have found significant evidence of Mars having a watery past with a much stronger magnetic field. Is it possible to find fossilized bacteria or something similar on the Martian surface without having to drill several meters?
Richard: If life existed on Mars in the distant past, there should be fossil evidence of those bacteria, and the best place to search would be in gypsum and other evaporate sedimentary rocks. For that reason, it's very important to have a sample return mission from Mars. Furthermore, since there's permafrost near the surface, and since we've found that microorganisms can remain alive and active in ice as long as the temp is above -40 C, there may well be life on Mars today in the polar ice caps and the permafrost within the upper layers of the Martian soil where the ice would periodically melt during the Martian summer.
(Moderator Jason): Thanks to everyone who posed questions today. We hope you found this to be very interesting and that you got some great answers. And a big thanks to Richard for taking some time to sit down with everyone and answer your questions! Have a great rest of your week.
Janet Anderson, 256-544-0034
Marshall Space Flight Center, Huntsville, Ala.