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Chemosynthetic Autotrophs

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Twenty-six hundred meters below our world of light, through the murky depths, resides a world completely alien to our own. It was not until 1977, when the first manned submarine was able to enter such depths and explore this oasis of life that resides around the earth’s nourishing thermal vents. Here, a vast community of organisms thrive under very harsh circumstances, and most importantly, in the absence of life-giving light. How is this possible? Chemoautotrophic microbes.

Chemoautotrophic bacteria are the primary producers on the ocean floor, where light cannot reach. Unlike most organisms, these bacteria do not need carbohydrates, vitamins, protein, and sugar to create energy, and ultimately to survive. Instead, these bacteria utilize an alternate source for synthesizing energy. This method is commonly known as chemosynthesis. Chemosynthesis is the process of making energy by oxidizing simple inorganic compounds. These compounds include reduced gases such as ammonia, sulfur, and methane. With the help of enzymes, energy can be made by breaking down these compounds and absorbing the valence electrons as shown in Diagram 1. (General 357) For chemosynthesis to occur, the perfect combination of inorganic compounds, oxygen, nitrogen-containing salts, and carbon must exist.

Currently, three different categories of chemoautotrophs, or “gas eaters” have been identified. The first are those that oxidize nitrogen compounds. These bacteria are predominantly found in lakes and swamps, where the soil is porous enough to allow ammonia, and other nitrous gases to escape. These chemoautotrophs are directly involved in the nitrogen cycle, because they use the organic nitrogen given off in the waste products of plants and animals to create energy. In turn, they give off a usable form of ammonia for the plants and animals to use. There is much diversity within these nitrogen bacteria that allow it to function more efficiently in its specific environment. Examples of this diversity can be noted by comparing Nitrospina and Nitrobacteria genuses. Nitrospinas are characterized by their long, slender, rod-like shapes. Internal membranes are scarcely found in this bacteria.

Nitrobacters are more diverse, and have been classified as being pear shaped. Unlike the Nitrospinas, Nitrobacters contain a multitude of internal membranes that help it efficiently use chemosynthesis. The chemosynthetic microbial world is not limited to these genus categories and characteristics. Their diversity of shapes, and sizes are immense. (Garden 128) The second major category of chemoautotrophs are the methane oxidizers, which play a vital role in the recycling of nutrients on our planet. These methane oxidizers use the methane found in heterotrophic organism’s waste product as their energy source. One can easily recognize these chemoautotrophs by the unpleasant scent they give off while breaking down the methane compounds for energy, often fuming in sewers and bogs. They also complete a cycle of chemical exchange between the the organism and these bacteria, which help decompose the wastes of organisms.

The third category is known as the sulfur oxidizers, which are prominently found in the ocean where hydrogen sulfide in in abundance. Sulfolobus acidocaldarius, the major bacteria of the thermal vents, have evolved accordingly to their extreme environment. It is so adapted to the near-boiling water found near these vents, that it will die if temperatures drop below 55 degrees Celsius. This is the result of an enzyme not being able to function when exposed to temperatures below 55 degrees Celsius. (NatGeo 123) Sulfur oxidizers play a large role in maintaining life near the thermal vents.

They are the primary producers of the thermal vents, and form bountiful symbiotic relationships with the larger organisms such as the tube worm. Since the discovery of life around thermal vents, more than three hundred new species have been discovered, and more are sure to follow. With the discovery of these self sustaining colonies without the aid of sunlight, scientists and astronomers are questioning the theory of life on other planets. A popular example of this is Europa, an ice covered moon which orbits around Jupiter. The possibility of life on Europa is based upon the the theory that chemoautotrophs could supply a vast community of organisms underneath Europa’s ice covered oceans.

Over the years, scientists have tried to study chemoautotrophs, but have had minimal success. The trouble with many species of microbes is that they can only survive in a flawless reproduction of their environment. For instance, sulfur oxidizing chemoautotrophs need a specific combination of sulfuric gases, carbon dioxide, temperature, and oxygen to survive. This combination of elements is very hard to maintain for an organism out of its habitat. As a result, scientists have limited opportunities, to study the behavior of these truly fascinating bacteria. A successful method used to study microbes, is the annualization of microbes via Alvin. Alvin is one of the most important and famous submarines in the marine science world. Alvin is composed of a titanium alloy frame, and is able to dive to depths past 8,000 feet below the surface in search of underwater communities. (Stover net article) Remote controlled water tanks attached to Alvin can encapsulate chemosynthetic microbes, and bring them back to the surface for further examination.

Scientists continue to research our earth, and interpret its evolution as a very violent planet. Early earth was exposed to a multitude of asteroid impacts, and the lack of a stable environment made earth opposed to life. The early oceans were shallow ad rocky, with near boiling temperatures. Due to the similarities of early earth, and the current habitat of the chemoautotrophs, a new theory was instilled. The discovery of chemosynthesis in bacteria gives new insight into how life may have been formed on earth. The theory currently accepted and taught is that photosynthesizers came first, and were followed by heterotrophs. This theory, however, was formulated before the discovery of Chemosynthetic microbes. This new synthesis process has questioned this theory, with solid arguments. Information that supports the theory that chemoautotrophs were the first forms of life on earth reflects that the elements and resources on early earth are much like those currently used for chemosynthesis in the ocean.

Another argument favors that chemosynthesis bacteria would have a “head start” on life, because these microbes could assemble its genetic makeup in sheltered areas, and avoid the destructive radiation given off by the sun when there was no atmosphere. (SciAmerican 81) It would seem unnecessary for life to create chemosynthesis, if photosynthesis was available for the first signs of life to use. However, a major flaw in this new theory of chemosynthesis life coming first, is that chemosynthesis involves the oxidation of simple compounds in order to create energy. This means that there had to be an adequate source of oxygen on earth before chemosynthetic autotrophs could survive. The process of oxidation also questions the true independent nature of chemoautotrophs, because it depends on oxygen from other photosynthetic life in order to maintain its existence. (Garden 129) Not even chemosynthetic bacteria can survive without the symbiosis from photoautotrophs, and ultimately, the sun.

Chemosynthetic autotrophs are very diverse in physical characteristics, but their methods for survival are quite synonymous. These microscopic producers seed the deep ocean with life, and are able to withstand a environment, unparalleled in severity. Chemosynthesis is an example of nature’s persistence to survive. With the combination of chemosynthesis and photosynthesis, it is difficult to imagine an environment on earth where life would have a problem sustaining life. Life will find a way.

Bibliography

1. “Into the Abyss.” Dir. Andrew Neal.

Atlantic Realm. Videocassette.

1989.

2. Hazen, Robert M. “Life’s Rocky Start” Scientific American April 2001: 77-85.

3. Lutz, Richard A. “Deep Sea Vents” National Geographic Oct 2000: 116-127.

4. Sagan, Dorion, and Lynn Margulis. Garden of Microbial Delights.

Dubuque, Iowa: Kendall/Hunt Publishing Co, 1993.

5. Schlegel, Hans G. General Microbiology.

New York: Cambridge UP, 1986.

6. Stover, Dawn. “Creatures of the Thermal Vents.” 6 May 2001.

Online Posting. Ocean Planet Smithsonian.

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7. Trotora, Gerard, Berdell Funke, Christine Case.

Microbiology: An Introduction. Menlo Park: Benjamin/Cummings Publishing, 1998.

8. Tyson, Peter “Living at Extremes.” Oct. 2000 Online posting. Nova Online. 6 May 2001 .

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