Archaebacteria: Life On Mars?

Wayne's WordIndexNoteworthy PlantsTriviaLemnaceaeBiology 101BotanySearch

Original Citation: Wayne's Word Noteworthy Plant For October 1997

Archaebacteria: A Life Form On Mars?

Remarkable Cells Live In Some Very Inhospitable
Places On Earth--Could They Survive On Mars?

© W.P. Armstrong [Updated 3 December 2010]

  1. Introduction To Life Forms In Extreme Envirnments
  2. Stromatolites In Glacier National Park, Montana
  3. Stromatolite Model At Biosphere 2 In Oracle, Arizona
  4. Modern-Day Stromatolites In Anza-Borrego State Park
  5. Desert Varnish In Alabama Hills Of Owens Valley
  6. Three Major Domains (Superkingdoms) Of Life
  7. Methane Producing Bacteria In Swamps
  8. Bacteria That Thrive In Boiling Hot Springs
  9. Owens Lake Colored Red By Halobacteria
  10. Are Halophiles The Most Ancient Of The Archaea?
  11. Evidence Of Life In A Martian Meteorite?
  12. Eubacteria Discovered Deep In A Gold Mine
  13. Bacterium In Mono Lake That Utilizes Arsenic
  14. References About Life In Extreme Environments

1. Introduction To Life Forms In Extreme Environments

Bacteria come in many shapes and sizes, from minute spheres, cylinders and spiral threads, to flagellated rods and filamentous chains. Although generally less than 5 micrometers long (smaller than human red blood cells) they are found practically everywhere and live in some of the most unusual and seemingly inhospitable places on earth.

All bacteria belong to the traditional kingdom Monera, characterized by unicellular or colonial prokaryotic cells lacking well-defined nuclei and membrane-bound organelles, and with chromosomes composed of a single, circular ring of DNA. Although they are placed in the same kingdom, these bacteria include several distinct divisions based on their unique cellular structure, including the eubacteria (true bacteria), cyanobacteria (blue-green algae) and archaebacteria. They survive in practically every conceivable habitat on earth, from boiling hot springs and steam vents at the bottom of the ocean to sun-baked boulders and salt crust of desert playas. Some forms have been living relatively unchanged on earth for over 3 billion years. The kingdom Monera has now been reorganized into two "superkingdoms" called domains, the Bacteria and Archaea. This classification revision is based on data from comparative studies of DNA and RNA. All the kingdoms of eukaryotes, including Protista (Protoctista), Fungi, Plantae and Animalia, are placed in the domain Eukarya. The large molecular differences between the majority of prokaryotes in the kingdom Monera and the archaebacteria warrants a separation based on categories above the level of kingdom. In other words, the differences between the true bacteria and archaebacteria are more significant than the differences between kingdoms of eukaryotes.

See 3-Domain System of Classification
Go To The Five Kingdoms of Life

Although there is evidence that prokaryotic bacteria (without nuclei) lived on earth 3.5 billion years ago, researchers at the University of Sydney and the Australian Geological Survey have recently discovered evidence that more complex cells with nuclei (eukaryotic cells) existed 2.7 billion years ago. They found a group of molecules called steranes, that are produced by eukaryoyic cells, in 2.7-billion-year-old rocks in Australia. The discovery of evidence for eukaryotic life so early in the earth's history, suggests that simpler prokaryotic cells may have lived even earlier than believed (over 3.5 billion years ago). [For more information about this subject see Science 13 August 1999.]

2. Ancient Stromatolites In Glacier National Park

Evidence of ancient cyanobacteria (also called blue-green algae) is provided by interesting rocklike formations of limestone called stromatolites. During countless centuries of time, calcareous sediments (limestone) and other materials are trapped in layers of filamentous colonies of cyanobacteria. Living stromatolites (appearing as reef-like domes in warm, shallow water) can still be seen to this day in Shark Bay, Australia and around certain islands in the Gulf of California. Exposed beds of these ancient fossilized "algal reefs" reveal a series of concentric layers where the cyanobacteria colonies once lived in shallow seas. The abundance of stromatolites in the fossil record is evidence that photosynthetic cyanobacteria were prevalent on earth, and played an important role in elevating the level of free oxygen in the earth's atmosphere. As one gazes at the spectacular limestone formations in Glacier National Park, Montana from Going-To-The-Sun Road, you are awe-struck with the enormous role these ancient cyanobacteria played as they removed carbon dioxide from primeval seas and precipitated it as massive calcium carbonate rocks. Releasing oxygen gas as a metabolic by-product, they must have been a major factor in producing the oxygen-rich atmosphere that allowed the development of other aerobic life forms on earth.

One billion-year-old stromatolites embedded in limestone along Going-To-The-Sun Road in Glacier National Park, Montana, USA. The concentric rings represent calcareous layers of limestone where ancient colonies of cyanobacteria once thrived in shallow seas.

Spherical precambrian stromatolites embedded in limestone from the Marble Mountains located in the arid Mojave Desert of San Bernardino County, California.

Any discusion of ancient life would be incomplete without mentioning a remarkable discovery made in a deep mine shaft near Carlsbad, New Mexico. Bacterial spores of the genus Bacillus were isolated from pockets (inclusions) in salt crystals harvested from an underground salt bed 2,000 feet below the surface. The salt deposits were formed from an ancient sea in a geologic formation that dates back about 250 million years. What is so remarkable about these spores is that microbiologists succeeded in growing them in a laboratory. The spores have survived in a cryptobiotic state millions of years before dinosaurs roamed the earth. Another microbe extracted directly from dissolved salt crystals appears to be related to the archaebacteria that thrive in the brine of present-day salt lakes. NASA is interested in ancient salt deposits because the planet Mars and Jupiter's moon Europa once had oceans and may have similar subterranean salt formations. Space missions in search of extraterrestrial life may eventually explore these ancient salt beds. For more about this significant discovery, see the article by R.H. Vreeland, W.D. Rosenzweig and D.W. Powers (2000), "Isolation Of A 250 Milion-Year-Old Bacterium From A Primary Salt Crystal," Nature 407: 897-900.


3. Stromatolite Model At Biosphere 2 in Oracle, Arizona

A fairly realistic stromatolite model at University of Arizona's Biosphere 2 in Oracle, Arizona. Note the dome-like structure composed of layers. The calcareous layers (lamellae) are produced by colonies of cyanobacteria living on the surface over countless centuries of time.


4. Living Stromatolites In Anza-Borrego Desert State Park

Living stromatolites have been found in Anza-Borrego Desert State Park of San Diego County. Two shallow, ephemeral (intermittent) streams have boulders and cobbles coated with calcareous layers and living colonies of mucilaginous, filamentous cyanobacteria. Several species of cyanobacteria grow on the surface of submersed rocks, including members of the Rivulariaceae (Calothrix, Rivularia and Gloeotrichia). According to H.P. Buchheim (personal communication, 2008), the stromatolite-forming cyanobacteria was originally identified as a species of Schisothrix in the Oscillatoriaceae, but was later confirmed as a species of Rivularia. The filaments of these cyanobacteria are covered with a slimy mucilaginous sheath. Calcareous sediments (limestone) and detrital stream particles are trapped in layers of filamentous colonies of the cyanobacteria. Over centuries of time, these encrusting layers (laminae) accumulate on the rocks and boulders, forming the stromatolites. Although the stromatolites are only up to two cm thick, they nevertheless form calcareous layers encrusting granite cobbles and boulders. The cyanobacteria utilize water, carbon dioxide and sunlight during photosynthesis. Byproducts of this process are oxygen and calcium carbonate (lime). Debris from the water is trapped in the slimy mucous coating (sheaths) of the filamentous bacterial mats and is gradually cemented together by the calcium carbonate. Presumably, intervals of creek desiccation facilitate in this cementation process, resulting in laminae composed of calcite and detrital stream particles. According to Buchheim (1995), these structures fulfill the criteria for identifying stromatolites: a knobby surface of digitate heads, lamination, internal calcification, and accretion due to the growth of mucilaginous cyanobacteria.

Stromatolite growth in Anza-Borrego Desert is most abundant in ephermeral sections of alkaline streams, including Carrizo and San Felipe Creeks, where maximum evaporation takes place and where solutes are the highest. The best formation of stromatolites was observed in areas where water flowed for only a few months in the spring of each year. The cyanobacterial mats apparently go into a dormant state when the creek becomes desiccated. According to Buchheim (1995), the major factor controlling stromatolite growth in these streams is high solute concentration as well as calcite supersaturation. What is interesting about the Anza-Borrego stromatolites is that it enables scientists to study colonies of these cyanobacteria which are truly "living fossils." Stromatolites are important from an evolutionary standpoint because they are frequently the subject of scientific discussions about the origin of life on earth. [Note: In Sentenac Canyon, tufa was observed instead of stromatolites. Tufa is a porous calcium carbonate deposit easily distiguished from stromatolites which are laminated.]

Tufa vs. Stromatolite

The calcareous precipitate on
this granite is called tufa. It was
deposited when the rock was
submersed in an alkaline lake.
Tufa does not have the layered
(laminate) structure of desert
stromatolites.

An ephemeral stream in Grapevine Canyon of Anza-Borrego Desert State Park. The submersed boulders and cobbles are encrusted with living colonies of stromatolite-forming cyanobacteria.

Cobbles from an ephemeral stream in Grapevine Canyon of Anza-Borrego Desert State Park. The rocks are covered with dense colonies of filamentous cyanobacteria of the order Oscillatoriales. Cyanobacteria such as these are responsible for the deposition of calcareous layers called stromatolites.

Magnified view of filamentous oscillatoriacean cyanobacteria resembling Rivularia living on submersed cobles in an ephemeral stream in Grapevine Canyon. Under ideal conditions, colonies of cyanobacteria similar to these are responsible for the deposition of calcareous layers known as stromatolites. Magnification 400x.

The following images were taken in Grapevine Canyon on 31 March 2007 during a very dry spring.
Shallow pools that once supported dense colonies of filamentous cyanobacteria on boulders and
cobbles were competely desiccated. The rocks were coated with a gray, knobby stromatolite layer
formed during previous years when the ponds were filled with supersaturated, calcium-rich water.

The boulders and cobbles in this image are all below the water level during wet years. They are coated with a knobby (bumpy) layer of calcium carbonate composed of microscopic laminae. The laminated calcifications were formed by dense colonies of filamentous cyanobacterica that grew on these rocks during previous wet seasons and meet Paul Buchheim's definition of stromatolites. In fact, the images closely resembles Dr. Buccheim's stromatolites in Carrizo Creek.

A boulder covered with stromatolites in Grapevine Canyon. The red arrow shows an area where the stromatolite coating has broken away, exposing the granitic core of the rock. During previous years this boulder was submersed in calcium-rich water and supported dense colonies of filamentous cyanobacteria.

Magnified view of stromatolite coating on granitic cobble showing laminate structure. The laminae are composed of white calcite, detrital stream particles, and an organic component composed of filamentous cyanobacteria. According to Buccheim (1995), the laminate structure is clearly distinguished from tufa, a porous calcareous precipitate that is common in desert alkaline streams. (10 x)


Highly magnified view of modern-day filamentous cyanobacteria (Anabaena azollae) from cavities within the leaves of the ubiquitous water fern (Azolla filiculoides). The larger, oval cells are heterocysts, the site of nitrogen-fixation where atmospheric nitrogen (N2) is converted into ammonia (NH3). The water fern benefits from its bacterial partner by an "in house" supply of usable nitrogen. The cellular structure of these bacteria has changed very little in the past one billion years. (500 x)


5. Desert Varnish In The Alama Hills & Anza-Borrego Desert

One of the most remarkable biogeochemical phenomena in arid desert regions of the world is desert varnish. Although it may be only a hundredth of a millimeter in thickness, desert varnish often colors entire desert mountain ranges black or reddish brown. Desert varnish is a thin coating (patina) of manganese, iron and clays on the surface of sun-baked boulders. Desert varnish is formed by colonies of microscopic bacteria living on the rock surface for thousands of years. The bacteria absorb trace amounts of manganese and iron from the atmosphere and precipitate it as a black layer of manganese oxide or reddish iron oxide on the rock surfaces. This thin layer also includes cemented clay particles which help to shield the bacteria against desiccation, extreme heat and intense solar radiation. It has been estimated that up to 10,000 years are required for a complete varnish coating to form on boulders in extreme arid desert regions.

Manganese varnish formation. Modified from Dorn & Oberlander,
1982. Reddish iron varnish develops in a similar oxidation reaction.

The sun-baked boulders of the Alabama Hills in Owens Valley, California are coated with a black layer of clay and manganese oxide precipitated by colonies of remarkable bacteria living on the rock surface.

The sun-baked boulders in the Colorado Desert of southern California are coated with a reddish-brown layer of clay and iron oxide precipitated by colonies of bacteria living on the rock surface. Native Americans once used the varnish surface to carve their elaborate petroglyphs.

See Article About Desert Varnish & Lichen Crust

Although they survive in some amazing environments, the previous examples of bacteria could not survive in the oxygen deficient atmosphere of Mars. However, there are bacteria that can survive without free oxygen under some of the most extreme environmental conditions on earth. Could any of these or related archaebacteria survive on the surface of Mars?

Does this picture resemble Anza Borrego Desert? The bleak and barren surface of Mars as seen from the Pathfinder Landing (photo courtesy of NASA). Could archaebacteria survive in this rocky, dusty landscape? [Note: The blue sky was added to photo using colorizing tool in HiJaak Pro.]

See Another Photo Of Mars Landscape
See Wayne's Word Images Of The Moon
More Wayne's Word Images Of The Moon

The Three Major Types Of Archaebacteria:

1. Methanogens (methane-producers)--responsible for swamp gas.

2. Extreme Thermophiles--live in hot springs and black smokers.

3. Extreme Halophiles--live in saturated brine and salt crust.

The five-kingdom system of classification for living organisms, including the prokaryotic Monera and the eukaryotic Protista, Fungi, Plantae and Animalia is complicated by the discovery of archaebacteria. The prokaryotic Monera include three major divisions: The regular bacteria or eubacteria; the cyanobacteria (also called blue-green algae); and the archaebacteria. Lipids of archaebacterial cell membranes differ considerably from those of both prokaryotic and eukaryotic cells, as do the composition of their cell walls and the sequence of their ribosomal RNA subunits. In addition, recent studies have shown that archaebacterial RNA polymerases resemble the eukaryotic enzymes, not the eubacterial RNA polymerase.

Archaebacteria also have introns in some genes, an advanced eukaryotic characteristic that was previously unknown among prokaryotes. In eukaryotic cells, the initial messenger RNA (M-RNA) transcribed from the DNA (gene) is modified (shortened) before it leaves the nucleus. Sections of the M-RNA strand called introns are removed, and the remaining portions called exons are spliced together to form a shortened (edited) strand of mature M-RNA that leaves the nucleus and travels to the ribosome for translation into protein. This process is known as "gene editing." Some authorities hypothesize that eukaryotic organisms may have evolved from ancient archaebacteria (archae = ancient) rather than from the common and cosmopolitan eubacteria. The archaebacteria could have flourished more than 3 billion years ago under conditions previously thought to be uninhabitable to all known life forms. Although many conservative references place the archaebacteria in a separate division within the kingdom Monera, some authorities now recognize them as a 6th kingdom--The kingdom Archaebacteria.


6. Three Domains (Superkingdoms) Of Living Organisms

In recent years, the traditional 5-kingdom or 6-kingdom system of classification has been challenged by authorities. Data from DNA and RNA comparisons indicate that archaebacteria are so different that they should not even be called a type of bacteria. Systematists have devised a classification level higher than a kingdom, called a domain or "superkingdom," to accomodate the archaebacteria. These remarkable organisms are now placed in the domain Archaea. Other prokaryotes, including eubacteria and cyanobacteria, are placed in the domain Bacteria. All of the traditional eukaryotic kingdoms are placed in the domain Eukarya. The 3-domain system of classification is shown in the following table:

Three Domains (Superkingdoms) Of Living Organisms
  I.  Bacteria: Most of the Known Prokaryotes

    Kingdom (s): Not Available at This Time

      Division (Phylum) Proteobacteria: N-Fixing Bacteria
      Division (Phylum) Cyanobacteria: Blue-Green Bacteria
      Division (Phylum) Eubacteria: True Gram Posive Bacteria
      Division (Phylum) Spirochetes: Spiral Bacteria
      Division (Phylum) Chlamydiae: Intracellular Parasites
 II.  Archaea: Prokaryotes of Extreme Environments

    Kingdom Crenarchaeota: Thermophiles
    Kingdom Euryarchaeota: Methanogens & Halophiles
    Kingdom Korarchaeota: Some Hot Springs Microbes
III.  Eukarya: Eukaryotic Cells

    Kingdom Protista (Protoctista)
    Kingdom Fungi
    Kingdom Plantae
    Kingdom Animalia


Domain: Archaea

7. Archaea: Methanogenic Bacteria

Methanogenic bacteria live in marshes, swamps and your gastrointestinal tract. In fact, they are responsible for some intestinal gas, particularly the combustible component of flatulence. They produce methane gas anaerobically (without oxygen) by removing the electrons from hydrogen gas (H2):

4H2 + CO2 = CH4 + 2H2O

The electrons and H+ ions from hydrogen gas are used to reduce carbon dioxide (CO2) to methane (CH4). In the reaction, the H+ ions combine with the oxygen from CO2 to form water (H2O). During this process, the electrons are shuttled through an anaerobic electron transport system within the bacterial membrane which results in the phosphorylation of ADP (adenosine diphosphate) to form ATP (adenosine triphosphate). ATP is the vital energy molecule of all living systems which is absolutely necessary for key biochemical reactions within the cells. In fact, the varnish bacteria make their ATP in a similar fashion, only the electrons are coming from the aerobic oxidation of iron and manganese. During the oxidation process, the electrons are shuttled through an iron-containing cytochrome enzyme system on the inner bacterial membrane. The actual synthesis of ATP from the coupling of ADP (adenosine diphosphate) with phosphate (PO4) is a lot more complicated and involves a mechanism called chemiosmosis. The electron flow generates a higher concentration (charge) of positively-charged hydrogen (H+) ions (or protons) on one side of the membrane. When one side of the membrane is sufficiently "charged," these protons recross the membrane through special channels (pores) containing the enzyme ATP synthetase, as molecules of ATP are produced. In eukaryotic cells, including the cells of your body, ATP is produced by a similar process within special membrane-bound organelles called mitochondria. In fact, some biologists believe that mitochondria (and chloroplasts) within eukaryotic animal and plant cells may have originated from ancient symbiotic bacteria that were once captured by other cells in the distant geologic past. This fascinating idea is called the "Endosymbiont Hypothesis."


8. Archaea: Thermophilic Bacteria

Extreme thermophilic bacteria live in boiling water of hot springs where no other living cells can possibly survive (i.e. without their proteins becoming completely denatured). They have also been discovered in (or near) hot water emanating from sulfide chimneys ("black smokers") thousands of feet deep at the bottom of the ocean (near the Galapagos Islands). Surviving in the wild near steam vents where the temperature reaches 350 degrees Celsius under tremendous pressure, the bacteria have also been cultured under extreme heat and pressure in the laboratory. Although their optimal "operating temperature" is just over 100 degrees Celsius, no one would have believed that a living cell containing DNA, RNA and protein could survive anaerobically in a pressure cooker at 250 degrees Celsius, more than twice the temperature of boiling water. These cells could easily have flourished on a young earth under conditions previously thought to be uninhabitable to all known life forms.


Bacteria Of Boiling Hot Springs In Yellowstone National Park

Boiling hot springs in Yellowstone National Park are colored by colonies of thermophilic cyanobacteria, eubacteria and archaebacteria. Orange-colored cyanobacteria generally occur in water that has cooled below 73 degrees Celsius (163 degrees F). The green chlorophylls in these photosynthetic bacteria are masked by orange carotenoid pigments. Like the bright red halobacteria of salt lakes, carotenoids protect the delicate cells from intense solar radiation, especially during the summer months. Warmer, whitish areas of the ponds contain stringy masses of nonphotosynthetic eubacteria. Thermus aquaticus survives in temperatures too high for photosynthetic bacteria, up to 80 degrees Celsius (176 degrees F). Thermus aquaticus is heterotrophic and survives on minute amounts of organic matter in the water. TAQ polymerase used in the amplification of DNA using the polymerase chain reaction (PCR) was originally isolated from a colony of T. aquaticus collected in a hot spring at Yellowstone National Park.

See Wayne's Word Article About Polymerase Chain Reaction (PCR)

A boiling hot springs in Yellowstone National Park. The orange-red coloration is caused by dense colonies of photosynthetic cyanobacteria.

Archaebacteria thrive in boiling water at Yellowstone National Park, at temperatures of 92 degrees Celsius (198 degrees F). These bacteria also thrive near steam vents at the bottom of the ocean at temperatures exceeding 115 degrees Celsius (239 degrees F). Scientists from throughout the world are studying the amazing bacteria flora at Yellowstone National Park. This is one of the best places on earth to study these organisms in their natural protected habitats. In other parts of the world, similar hot springs have been destoyed for the production of geothermal energy.

Boiling hot springs in Yellowstone National Park. The orange-red coloration is caused by thriving colonies of photosynthetic cyanobacteria. Stringy masses of nonphotosynthetic eubacteria occur in the whitish areas of warmer water.

Acid hot springs in Yellowstone National Park with a pH of below 4.0 support the eukaryotic alga Cyanidium caldarum. This remarkable photosynthetic alga can even survive in a pH of zero! Some acidophilic hot springs bacteria utilize the oxidation of sulfur and iron for the synthesis of ATP. Alkaline hot springs support colonies of bacteria that utilize hydrogen sulfide for their energy source.

Major Divisions Of Bacteria Within The Kingdom Monera

Life as we know it may have first arisen more than three billion years ago in a high temperature environment of boiling water. Thermophilic bacteria in hot springs of Yellowstone National Park may be relict populations of the first life on earth. In fact, these thermophilic bacteria may be the ancestors of all other life forms, including humans!


9. Archaea: Halophilic Bacteria

The third group of archaebacteria (called halobacteria) are especially interesting because they color the salt flats of desert playas and evaporation ponds a spectacular pinkish-red. This is especially evident in Owens Lake in the arid Owens Valley of California. Owens Lake was once a vast blue lake, before it was drained (by diverting Owens River) to provide the city of Los Angeles with water. Today it is a pinkish-red, dry lake bed or playa teaming with salt-loving archaebacteria. Solar evaporation ponds in the salt flats along US Highway 395 sometimes become a deep vermilion red. A drop of brine contains millions of tiny rod-shaped bacteria swimming among cuboidal crystals of sodium chloride (NaCl). Two flagellated halophilic green algae (Dunaliella and Dangeardinella) are often mixed with the rod-shaped halobacteria. Although Dunaliella in some regions of the world is also colored bright red, the populations in Owens Lake are green. The bacteria thrive in saturated brine up to 30 percent salinity (9 times the salinity of sea water). They can also be found embedded in the thick, pinkish-red salt crust literally baking in the desert sun. Because of their high internal osmotic concentration of potassium and sodium ions they are able to survive in the brine, otherwise they would rapidly become plasmolyzed and shrivel up. In fact, they cannot survive if the salt concentration drops below 10 percent. The bright red carotenoid pigment protects the cells from intense solar radiation. In some arid salt flats (such as Australia) the carotene-rich halobacteria and halophilic algae are harvested as a source of B-carotene, the precursor of vitamin A.

The vivid red brine (teaming with halophilic archaebacteria) of Owens Lake contrasts sharply with the gleaming white deposits of soda ash (sodium carbonate). The picturesque Inyo Range can be seen in the distance.

Tubes of red brine from Searles Lake, a salt lake in the arid Mojave Desert of California. The test tube on right was spun in a centrifuge at 5,000 rpm, forcing all the red halobacteria into a compact mass at the bottom.

Numerous deep basins east of California's Sierra Nevada contain dry lake beds or playas. In the distance in this aerial view are Saline Valley and the Inyo Range, with the snow-covered Sierra Nevada crest beyond. Some of the salt lakes and ponds in these playas have become seeded with airborne spores or cells of salt-loving (halophilic) algae and pinkish-red archaebacteria.

Aerial view over the Great Salt Lake, Utah at an altitude of about 7,000 feet. The red coloration is caused by halophilic archaebacteria and possibly red Dunaliella (possibly D. salina). [Photo taken by E. M. Armstrong sitting in the window seat of a Boeing 767.]

Another remarkable pigment in the cell membrane of halobacteria called (bacteriorhodopsin) enables them to utilize sunlight for energy. Like photosynthetic chloroplasts in plant cells, the halobacteria produce their own ATP; but unlike green plants, they utilize bacteriorhodopsin instead of chlorophyll. The exact mechanism of ATP production is complicated and beyond the scope of this article, but it involves a "proton pump" across their cell membrane similar to the chemiosmotic mechanism for ATP synthesis in the chloroplasts and mitochondria of eukaryotic cells in higher organisms. Positively-charged hydrogen ions (protons), forced to one side of the membrane, flow back through special channels (pores) in the membrane as ATP (adenosine triphosphate) is enzymatically produced from ADP (adenosine diphosphate) and P (phosphate). These bacteria are especially interesting because the chemiosmotic mechanism for generating ATP does not require an electron transport system as in other photosynthetic bacteria and higher plants. Strains of these amazing bacteria have also been shown to survive anaerobically without free atmospheric oxygen while deeply embedded in thick salt crust. Bacteriorhodopsin is remarkably similar to the light sensitive pigment (rhodopsin) in the rod cells of human eyes which enables us to see in dim light. Thus, when we enter a dimly lighted room, it takes about 30 minutes for our eyes to adjust fully as the rhodopsin gradually increases in concentration. Of course, a flash of light can instantaneously break down your rhodopsin level, much to the chagrin of star-gazers who have become accustomed to the darkness.

Drawing of highly magnified view (2000X) of brine showing rod-shaped salt-loving bacteria (Halobacterium) and two species of halophilic green algae (Dunaliella salina and Dangeardinella saltitrix) swimming among cuboidal crystals of sodium chloride. The latter species has a smaller, slender, pear-shaped cell with two peculiar flagella, one extending forward and one trailing behind. A single drop of brine may contain literally millions of the minute bacteria.

To appreciate the tenacity of halophilic cells, I once sent some pieces of salt crust from Owens Lake to Dr. Richard Norris, an expert on flagellates at the University of Witwatersrand in Johannesburg, South Africa. Dr. Norris was able to dissolve the salt crystals and extract the algal cells which he identified as Dangeardinella saltitrix. This species has a slender, pear-shaped cell with two peculiar flagella, one extending forward and one trailing behind. Extreme halophilic algal cells such as Dangeardinella and pinkish-red halobacteria (Halobacterium) can survive completely encased in salt crust for extended periods of time. In fact, bacterial spores of the genus Bacillus were isolated from pockets (inclusions) in salt crystals harvested from an underground salt bed 2,000 feet below the surface. The salt deposits were formed from an ancient sea in a geologic formation that dates back about 250 million years.

These pinkish-red crystals of sodium chloride (NaCl) are colored by millions of halobacteria. The bacteria survive inside the salt crust, even though it has been exposed to sun-baked summers and freezing winters in California's Owens Valley.


10. Are Halophiles The Most Ancient Of The Archaea?

A recent article in Astrobiology Magazine (May 19, 2004) by Leslie Mullen reports that halobacteria may be the oldest life form on earth. Professor Shiladitya DasSarma of the University of Maryland Biotechnology Institute is studying the evolution of these red salt-loving bacteria. DasSarma and his team have recently sequenced the genome of the extreme halophile called Halobacterium NRC-1. When compared with the genes of other organisms, Halobacterium NRC-1 appears to be the most ancient of the archaean group. Comparisons of small ribosomal RNA sequences indicate that halophilic bacteria are closely related to the methanogens. Both types of bacteria are now classified in the kingdom Euryarchaeota within the Archaea domain. Halophiles need oxygen while methanogens are anaerobic; however, halophiles can produce energy without oxygen in two ways: from the degradation of arginine, and by using the photosynthetic molecule bacteriorhodopsin (see above). It has been suggested that these two methods of anerobic energy production are the last remnants from the halophile's anaerobic ancestry when the earth's atmosphere lacked free oxygen gas more than 2 billion years ago.

One perplexing question about the evolution of life is whether the first cells appeared in fresh or warm saline waters. If anaerobic halophiles turn out to be the most ancient life form on earth, perhaps they also occur on Mars. When Mars lost most of its water though evaporation it became very salty. According to DasSarma, there may still be halophiles trapped in brine inclusions within salt crystals. Another survival adaptation of extreme halophiles is their exceptional resistance to solar radiation. Perhaps there may be some validity to the Panspermia Hypothesis which states that life originated elsewhere and was transferred to earth by meteors.

More Information About Halobacteria:
University of Maryland Halobacteria Project


11. Evidence Of Life In A Martian Meteorite?

In 1984, a 4.2-pound, potato-sized meteorite called ALH84001 was discovered in Allan Hills ice field, Antarctica, by an expedition of the National Science Foundation's Anarchic Meteorite Program. Since its discovery, the meteorite has been analyzed by a NASA research team at the Johnson Space Center and at Stanford University using sophisticated high-resolution scanning microscopy and laser mass spectrometry. The rock is believed to have originated underneath the Martian surface between 3.6 and 4 billion years ago, a time when it is generally thought that the planet was warmer and wetter. In fact, water is believed to have penetrated fractures in the subsurface rock, possibly forming an underground water system. Then, 15 million years ago, a huge comet or asteroid struck Mars, ejecting a piece of the rock from its subsurface location with enough force to escape the planet's gravity. For millions of years, the chunk of rock floated through space. It encountered earth's atmosphere 13,000 years ago and fell in Antarctica as a meteorite.

Evidence for subsurface deposits of water on Mars was substantiated by studies published in the journal Science May 2002. Data from the Mars Odyssey spacecraft suggest that large deposits of ice are buried just one to two feet (0.3 m to 0.6 m) below the planet's surface. The recent findings corroborate earlier studies that showed strong evidence that Mars was once covered with water. The planet has valleys, gullies and channels, characteristic evidence of the flow of water. The new studies suggest that the water may have drained downward until it was trapped as ice just below the protective layer of soil. The presence of water on Mars increases the odds that microbial life once existed on the planet.

Go To Reference Site About Life On Mars

Evidence of ancient life in the meteorite includes tiny globs of carbonates, organic compounds called polycyclic aromatic hydrocarbons (PAHs) and mineral compounds (iron sulfides and magnetite) that are commonly produced by anaerobic bacteria and other microbes on earth. In addition, these compounds were found in locations associated with fossil-like structures strikingly similar in appearance and size to microscopic fossils of the tiniest bacteria found on earth. The presence of carbonates near these imprints is similar to fossilized limestone deposits on earth. When microorganisms die, their complex molecules often degrade into PAHs. Not only did the NASA scientists find PAHs, but they found these molecules concentrated in the vicinity of the carbonate globules. For more information and photographs about this remarkable discovery, please refer to the following NASA web sites:

NASA Life On Mars Website
NASA Life On Mars Website Photos
WAYNE'S WORD Photo Of Life On Mars


12. Amazing Eubacteria Discovered Deep In A Gold Mine

In addition to the archaebacteria, there are also species of eubacteria that live and multiply under some of the most extreme environmental conditions on earth. For example, bacteria in the gram-positive genus Deinococcus are resistant to levels of radiation that would kill many life forms. A decade ago, scientists considered it impossible for life to exist deep in the earth's surface, in furnace-like rock heated by the earth's interior to temperatures of 131 to 140 degrees Fahrenheit (55-60 degrees Celsius). Biologists also believed that organisms needed a steady supply of nutrients, oxygen and a constant source of energy from the surface just to survive. But during the past ten years, modified oil drills have penetrated supposedly sterile rock two miles below the surface and actually retrieved living bacteria. The microbes had apparently been living for millions of years on little more than water, hydrogen, sulfur, and iron-rich minerals in the rock. Scientists have also found strange bacteria living deep within a South African gold mine near Johannesburg. The bacteria were collected in organically-rich, blackened veins in the rock containing gold, uranium and iron pyrite. Some researchers think the bacteria may actually be deriving energy from natural radioactivity in these rocks. They may also be living on the iron pyrite, oxidizing it to ferric iron and sulfate, while precipitating the gold.

There are also thermophilic eubacteria, including the genus Thermus, that live in the boiling water of hot springs. In fact, a new species of Thermus was recently isolated from hot water trapped in rocks deep in the South African gold mine discussed above. These recent discoveries of subterranean bacteria isolated from the surface for millions of years offer compelling evidence to suggest that life could exist below the surface of Mars, a planet that once had water flowing freely on its now-barren surface. For a nice summary of these recent discoveries, refer to The Chronicle of Higher Education, August 6, 1999 (http://chronicle.com).

Summary Of Bacteria Tolerant Of Environmental Extremes:

  1.  Some species can survive without free atmospheric oxygen.

  2.  Some species can produce ATP from sunlight without oxygen.

  3.  Some species can oxidize inorganic minerals to obtain their ATP.

  4.  Some species can survive enormous temperature extremes.

  5.  Some species can survive high doses of radiation (radioactivity).

  6.  Some species survive in rocks and water pockets deep in the earth.  

One of the driest places on earth is the Atacama desert of Chile that occurs in the vast rain shadow of the Andes. In fact, the bleak and extreme arid conditions of this harsh environment have been compared with Mars. Although no visible life forms occur on soil or rock surfaces, researchers have found endolithic bacteria associated with desert varnish (Kuhlman, et al. 2008). Wierzchos, et al. 2006 also found photosynthetic cyanobacteria (Chroococcidiopsis) living inside halite rocks that absorb trace amounts of moisture from the atmosphere. These discoveries of endolithic life may have implications for the discovery of life below the Martian surface.

So the bottom line here is: Could archaebacteria (or perhaps another type of eubacteria) possibly survive on Mars? Some of these bacteria need no organic nutrients to live, only inorganic ions and light. Some don't even need light--they simply oxidize inorganic minerals to get their energy (ATP). Some can thrive in the crushing pressures of the deepest oceans and in rocks below the earth's surface; and others at a pH as low as 1 or as high as 12. Some can even survive high doses of radiation or starvation for hundreds of years. With the possible exception of extreme subzero temperatures, could any of these remarkable bacteria survive in the extreme environmental conditions on the red planet? And perhaps more importantly, is it necessary to sterilize space exploration vehicles sent to Mars in order to prevent bacterial infection of our neighboring planet? Hopefully, future Mar's probes will provide answers to some of these intriguing questions--answers that could have a profound impact on our perception of the universe.

Go To A Reference Site About Life On Mars


13. Bacterium That Utilizes Arsenic Instead Of Phophorus Discovered In Mono Lake

Calcareous tufa towers at mono lake. The highly alkaline water is also rich in arsenic.

Life on Earth is mostly composed of the six elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. These elements make up the major compounds of living systems, including nucleic acids, proteins and lipds. Felisa Wolfe-Simon and her Nasa astrobiology team (Science DOI: December 2010) discovered a unique bacterium in the saline waters of Mono Lake that utilizes the toxic element arsenic intead of phosphorus. The bacterium is named GFAJ-1, and it belongs to the moderately halophilic (salt-loving) family Halomonadaceae. It is in the domain Bacteria, division (phylum) Proteobacteria, class Gammaproteobacteria.

Arsenic is in the same chemical group as phosphorus (group 15) in the periodic table of elements. Arsenic ions are notoriously deadly to multicellular organisms because of their interaction with protein thiols. A bacterium that can incorporate arsenic into its major organic compounds in the place of phosphorus presents some fascinating speculation in the field of astrobiology. This is another example of a life form that could possibly survive in hostile environments where no organism has previously thought to survive.

References

  1. Brock, T.D. 1994. Life At High Temperatures. Yellowstone Association For Natural Science, History and Education, Inc.

  2. Brock, T.M. and M.T. Madigan. 1988. Biology of Microorganisms (5th Edition). Prentice Hall, Englewood Cliffs, New Jersey.

  3. Buchheim, H.P. 1995. "Stromatolites: Living Fossils In Anza-Borrego Desert State Park." Pages 119-124 in: Paleontology and Geology of the Western Salton Trough Detachment, Anza-Borrego Desert State Park, California (Volume I). P. Remeika and A. Sturz, Editors. San Diego Association of Geologists, San Diego, California.

  4. DiGregorio, B. 1997. Mars: The Living Planet. Frog Ltd., Berkeley, California.

  5. Dorn, R.I. and T.M. Oberlander. 1981. "Microbial Origin of Desert Varnish." Science 213: 1245-1247.

  6. Dorn, R.I. and T.M. Oberlander. 1982. "Rock Varnish." Progress In Physical Geography 6: 317-367.

  7. Grant, W.D., R.T. Gemmell and T.J. McGenity. 1998. "Halobacteria: The Evidence For Longevity." Estremophiles 2: 279.

  8. Kuhlman, K.R., Venkat, P., La Duc, M.T., Kuhlman, G.M., and C.P. McKauy. 2008. "Evidence of a Microbial Community Associated with Rock Varnsish at Yungay, Atacama Desert, Chile." Journal of Geophysical Research Vol. 113.

  9. Prescott, L.M., J.P. Harley and D.A. Klein. 1996. Microbiology (Third Edition). Wm. C. Brown Publishers, Dubuque, Iowa.

  10. Schulze-Makuch, D., Fairén, A.G., and A.F. Davila. 2008. "The Case for Life on Mars." International Journal of Astrobiology 7(2): 117-141.

  11. Stoeckenius, W. 1976. "The Purple Membrane of Salt-Loving Bacteria." Scientific American 234: 38-46.

  12. Wierzchos, J., Ascaso, C., and C.P. McKay. 2006. "Endolithic Cyanobacteria in Halite Rocks from the Hyperarid Core of the Atacama Desert. Astrobiology 6 (3): 415-422.

  13. Woese, C.R. 1981. "Archaebacteria." Scientific American 244: 98-122.

  14. Wolfe-Simon, F., et al. 2010. "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus." Science DOI: 10.1126/science.1197258.

Return To Fossils Of Ancient Plants Page
Return To WAYNE'S WORD Home Page
Return To NOTEWORTHY PLANTS Page
Go To Biology GEE WHIZ TRIVIA Page
Go To The LEMNACEAE ON-LINE Page