User:Katherinethomas1: Difference between revisions
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=Introduction= | =Introduction= | ||
[http://en.wikipedia.org/wiki/Antarctica Antarctica] offers nearly no opportunity for colonization, as it is almost entirely covered by ice <ref name="Lay09"> Laybourn-Parry | [http://en.wikipedia.org/wiki/Antarctica Antarctica] offers nearly no opportunity for colonization, as it is almost entirely covered by ice.<ref name="Lay09">Laybourn-Parry, J. (2009). Microbiology. No place too cold. Science (New York, N.Y.), 324(5934), 1521.</ref> | ||
. However, in the ice-free areas of the continent, lakes can exist <ref name="Lay09" /> | . However, in the ice-free areas of the continent, lakes can exist. <ref name="Lay09" /> These lakes vary in composition, ranging from freshwater to hyper saline, as well as being either permanently covered with ice, such as subglacial lakes, or depending on the season, temporarily covered with ice. <ref name="Lay02"> Laybourn-Parry, J. (2002). Survival mechanisms in antarctic lakes. Philosophical Transactions of the Royal Society of London.Series B: Biological Sciences, 357(1423), 863-869 </ref> Research of these lakes provides new findings for microorganisms that can persist in these extreme environments, and have yet to be discovered elsewhere. | ||
<br /> | <br /> | ||
<br /> | <br /> | ||
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==Types of Lakes== | ==Types of Lakes== | ||
Both subglacial and open lakes exist in Antarctica. Subglacial lakes are liquid water bodies that can be found under glaciers, ice caps or ice sheets. ( | Both subglacial and open lakes exist in Antarctica. Subglacial lakes are liquid water bodies that can be found under glaciers, ice caps or ice sheets. <ref name="Priscu"> Priscu, J. C., Tabacco, I., Kennicutt, M. C., Bell, R. E., Bulat, S. A., Ellis-Evans, J. C., and Siegert, M. J. (2005). </ref> Exploring subglacial antarctic lake environments. Eos, Transactions American Geophysical Union,86(20), 193. The largest of these lakes is [http://en.wikipedia.org/wiki/Lake_vostok Lake Vostok], which is covered by a 4km thick ice sheet <ref name="Priscu" />. The ice cover restricts interaction between the lake and the exterior environment <ref name="Cowan"> Cowan, D. A., and Tow, L. A. (2004). Endangered antarctic environments. Annual Review of Microbiology, 58(1), 649-690. </ref> However, open lakes are not ice-covered, and usually have high salt concentrations. <ref name="Cowan" /> | ||
[[File:Soybean.jpg|thumb|x200px|right|Soybeans prior to soy milk production]] | [[File:Soybean.jpg|thumb|x200px|right|Soybeans prior to soy milk production]] | ||
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==Salinity== | ==Salinity== | ||
There are a number of both fresh and saline water lakes in Antarctica. Saline lakes contain a total of 3% dissolved salts ( | There are a number of both fresh and saline water lakes in Antarctica. Saline lakes contain a total of 3% dissolved salts. <ref name="Burton"> Burton, H. R. (1981). 24. chemistry, physics and evolution of antarctic saline lakes: A review. Hydrobiologia, 81-82(1), 339-362. </ref> Steep gradients of salt concentration are present in these lakes, making them [http://en.wikipedia.org/wiki/Meromictic meromictic], resulting in different niches within the lake. <ref name="Cowan" /> As well, freshwater lakes tend to average between 1-2 degrees Celsius, while saline lakes average below 0 degrees Celsius. <ref name="Lay02" /> | ||
==Light== | ==Light== | ||
Availability of light depends on the thickness of ice covering the lake, if present. Solar radiation can be transmitted through thin ice sheets, but ice sheets of around 4-6m thick prohibit light penetration | Availability of light depends on the thickness of ice covering the lake, if present. Solar radiation can be transmitted through thin ice sheets, but ice sheets of around 4-6m thick prohibit light penetration. <ref name="Cowan" /> Low light levels correspond to low levels of photosynthesis, which may not be sufficient for microbial growth.<ref name="Lay09"> | ||
==Oxygen== | ==Oxygen== | ||
Oxygen is carried into the lakes through melting glaciers (Wharton et al 1986). As well, photosynthesis by benthic mat microbes provides the system with dissolved O2 | Oxygen is carried into the lakes through melting glaciers (Wharton et al 1986). As well, photosynthesis by benthic mat microbes provides the system with dissolved O2.<ref name="Lay09" /> O2 gradients form in the lakes, with very high concentrations near the surface (or under the ice cover, if present), and anoxic environments at the bottom. <ref name="Cowan" /> | ||
=Microbial Processes= | =Microbial Processes= | ||
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==Carbon Cycle== | ==Carbon Cycle== | ||
Carbon is a building block for many molecules, and is found in all living organisms. In a lake’s anoxic environment, methanogens are able to use acetate, H2, and CO2 for fermentation, leading to the formation of methane ( | Carbon is a building block for many molecules, and is found in all living organisms. In a lake’s anoxic environment, methanogens are able to use acetate, H2, and CO2 for fermentation, leading to the formation of methane.<ref name="Wilkins"> Wilkins, D., Yau, S., Williams, T. J., Allen, M. A., Brown, M. V., DeMaere, M. Z., and Cavicchioli, R. (2013). Key microbial drivers in antarctic aquatic environments. FEMS Microbiology Reviews, 37(3), 303-335. </ref> Where oxygen is available, phytoplankton uptake carbon during photosynthesis, converting CO2 into organic carbon.<ref name="Lay09" /> Organic carbon from decomposing plankton, or other benthic microorganisms, is usually segregated into sediment through the process of [http://en.wikipedia.org/wiki/Sedimentation sedimentation]. <ref name="Wharton">Wharton, J.,R A., McKay, C. P., Simmons, J.,G M., and Parker, B. C. (1986). Oxygen budget of a perennially ice-covered antarctic lake. Limnology and Oceanography, 31(2), 437. </ref> As well, viruses lyse host cells to return carbon to the carbon pool in its inorganic form, which then gets transferred to protozoa in the system. <ref name="Lay09" /> | ||
==Nitrogen Cycle== | ==Nitrogen Cycle== | ||
Nitrogen is important for all organisms, as it is makes up nucleic and amino acids, which are essential for life. Fixed nitrogen enters lakes when glacial streams melt | Nitrogen is important for all organisms, as it is makes up nucleic and amino acids, which are essential for life. Fixed nitrogen enters lakes when glacial streams melt. <ref name="Cowan" /> This nitrogen then becomes available for cyanobacteria to use for [http://en.wikipedia.org/wiki/Nitrogen_fixation nitrogen fixation] (Cowan and Tow 2004). Different processes of the nitrogen cycle are separated into different areas of the lake. When ammonium diffuses from anoxic layers, nitrifying bacteria use that ammonium to produce nitrate at the border between oxic and anoxic water. <ref name="Howard"> Howard-Williams, C., and Hawes, I. (2007). Ecological processes in antarctic inland waters: Interactions between physical processes and the nitrogen cycle. Antarctic Science, 19(2), 205-217.</ref> When nitrate and nitrous oxide diffuse into the anoxic layers, denitrification occurs. <ref name="Howard" /> Decomposition also occurs within the anoxic layer, which releases ammonium through sulphate reduction. <ref name="Howard" /> | ||
=Key Microorganisms= | =Key Microorganisms= | ||
Antarctic lakes do not have large food chains, as no fish are present, resulting in microbes dominating the system | Antarctic lakes do not have large food chains, as no fish are present, resulting in microbes dominating the system. <ref name="Lay02"> | ||
==Cyanobacteria== | ==Cyanobacteria== | ||
[http://en.wikipedia.org/wiki/Cyanobacteria Cyanobacteria] are the major components of benthic phototrophs, which take part in forming mats at the bottom of lakes that range in thickness from a few micrometeres to a few decimeteres (Sabbe et al 2004). A large number of cyanobacteria can make up these mats; especially members of Oscillatoriales, and all these bacteria take part in oxygenic photosynthesis, as well as nitrogen fixation in these lakes | [http://en.wikipedia.org/wiki/Cyanobacteria Cyanobacteria] are the major components of benthic phototrophs, which take part in forming mats at the bottom of lakes that range in thickness from a few micrometeres to a few decimeteres (Sabbe et al 2004). A large number of cyanobacteria can make up these mats; especially members of Oscillatoriales, and all these bacteria take part in oxygenic photosynthesis, as well as nitrogen fixation in these lakes. <ref name="Wilkins" /> [http://en.wikipedia.org/wiki/Microbial_mats Microbial mats] are beneficial to cyanobacteria, as it allows for close interactions between the organisms. <ref name="Wilkins" /> This association allows for better growth of the community as a whole, compared to an isolated bacterium, as metabolic processes of different organisms are combined. <ref name="Wilkins" /> | ||
==Phytoplankton== | ==Phytoplankton== | ||
| Line 50: | Line 50: | ||
Nutritionally, soy milk is quantitatively similar to cows milk. The major difference is the lower sugar content, which contributes to an overall lower level of carbohydrates. <br /> | Nutritionally, soy milk is quantitatively similar to cows milk. The major difference is the lower sugar content, which contributes to an overall lower level of carbohydrates. <br /> | ||
[http://en.wikipedia.org/wiki/Phytoplankton Phytoplankton] are adapted to survive in the Antarctic lake environments of low light and temperatures, and use photosynthesis for growth | [http://en.wikipedia.org/wiki/Phytoplankton Phytoplankton] are adapted to survive in the Antarctic lake environments of low light and temperatures, and use photosynthesis for growth. <ref name="Lay09" /> However, when photosynthesis is not enough to sustain the organism, so mixotrophy is used for survivial.<ref name="Lay02" /> This method involves growing on mixed nutrients, and the use of both autotrophy and heterotrophy. <ref name="Lay09" /> Along with the use of photosynthesis, the organism grows on bacteria and dissolved organic carbon.<ref name="Lay02" /> The use of mixotrophy is essential for phytoplankton survival, especially in times or areas, of low sunlight.<ref name="Lay02" /> | ||
==Viruses== | ==Viruses== | ||
There is an abundance of viruses in Antarctic Lakes, and these viruses are thought to influence the lake’s food chains by being one of the main methods of regulation of microbial organisms | There is an abundance of viruses in Antarctic Lakes, and these viruses are thought to influence the lake’s food chains by being one of the main methods of regulation of microbial organisms. <ref name="Lopez"> López-Bueno, A., Tamames, J., Velázquez, D., Moya, A., Quesada, A., and Alcamí, A. (2009). High diversity of the viral community from an antarctic lake. Science (New York, N.Y.), 326(5954), 858-861. </ref> Some main viruses in these communities are single stranded DNA (ssDNA) viruses, which infect eukaryotes, and double stranded DNA (dsDNA) viruses, which infect algae. <ref name="Lopez" /> However, there is a large diversity of viruses in these lakes, many of which that have yet to be identified. <ref name="Lopez" /> | ||
=Current Research= | =Current Research= | ||
'''1''' Scientists are have recently researched the microbial diversity of a sediment sample from [http://en.wikipedia.org/wiki/Lake_Hodgson Lake Hodgson] ( | '''1''' Scientists are have recently researched the microbial diversity of a sediment sample from [http://en.wikipedia.org/wiki/Lake_Hodgson Lake Hodgson].<ref name"Pearce">Pearce, D.A., Hodgson, D.A., Thorne, M.A.S., Burns, G., and Cockell, C.S. (2013). Preliminary analysis of life within a former subglacial lake sediment in antarctica. Diversity, 5(3), 680-702.</ref> It was found that 77% of the microorganism diversity could be identified with previously found microbes, while 23% could not be recognized.<ref name="Pearce" /> This indicates that a large number of microbes still remain unknown to scientists. Further research is necessary to continue to reveal more information on the diversity of microbes, and how they continue to live in the extreme Antarctic Lake conditions. <ref name="Pearce" /> | ||
'''2''' Research in Deep Lake has demonstrated that [http://en.wikipedia.org/wiki/Horizontal_gene_transfer horizontal gene transfer] occurs quite frequently between microorganisms ( | '''2''' Research in Deep Lake has demonstrated that [http://en.wikipedia.org/wiki/Horizontal_gene_transfer horizontal gene transfer] occurs quite frequently between microorganisms. <ref name="Damaere">Demaere, M. Z., Woyke, T., Kyrpides, N. C., Tringe, S. G., Cavicchioli, R., Williams, T. J., and Davenport, K. W. (2013). High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated antarctic lake. Proceedings of the National Academy of Sciences of the United States of America, 110(42), 16939. </ref> Large DNA segments are exchanged between different classes of microorganisms, leading to evolution.<ref name="Damaere" /> This allows the microorganisms to avoid competition for resources, as the exchanged DNA helps with niche adaptation.<ref name="Damaere" /> | ||
=References= | =References= | ||
<references/> | <references/> | ||
Revision as of 23:03, 26 November 2013
Introduction
Antarctica offers nearly no opportunity for colonization, as it is almost entirely covered by ice.[1]
. However, in the ice-free areas of the continent, lakes can exist. [1] These lakes vary in composition, ranging from freshwater to hyper saline, as well as being either permanently covered with ice, such as subglacial lakes, or depending on the season, temporarily covered with ice. [2] Research of these lakes provides new findings for microorganisms that can persist in these extreme environments, and have yet to be discovered elsewhere.
Physical Environment
Types of Lakes
Both subglacial and open lakes exist in Antarctica. Subglacial lakes are liquid water bodies that can be found under glaciers, ice caps or ice sheets. [3] Exploring subglacial antarctic lake environments. Eos, Transactions American Geophysical Union,86(20), 193. The largest of these lakes is Lake Vostok, which is covered by a 4km thick ice sheet [3]. The ice cover restricts interaction between the lake and the exterior environment [4] However, open lakes are not ice-covered, and usually have high salt concentrations. [4]
Salinity
There are a number of both fresh and saline water lakes in Antarctica. Saline lakes contain a total of 3% dissolved salts. [5] Steep gradients of salt concentration are present in these lakes, making them meromictic, resulting in different niches within the lake. [4] As well, freshwater lakes tend to average between 1-2 degrees Celsius, while saline lakes average below 0 degrees Celsius. [2]
Light
Availability of light depends on the thickness of ice covering the lake, if present. Solar radiation can be transmitted through thin ice sheets, but ice sheets of around 4-6m thick prohibit light penetration. [4] Low light levels correspond to low levels of photosynthesis, which may not be sufficient for microbial growth.Cite error: Closing </ref> missing for <ref> tag Where oxygen is available, phytoplankton uptake carbon during photosynthesis, converting CO2 into organic carbon.[1] Organic carbon from decomposing plankton, or other benthic microorganisms, is usually segregated into sediment through the process of sedimentation. [6] As well, viruses lyse host cells to return carbon to the carbon pool in its inorganic form, which then gets transferred to protozoa in the system. [1]
Nitrogen Cycle
Nitrogen is important for all organisms, as it is makes up nucleic and amino acids, which are essential for life. Fixed nitrogen enters lakes when glacial streams melt. [4] This nitrogen then becomes available for cyanobacteria to use for nitrogen fixation (Cowan and Tow 2004). Different processes of the nitrogen cycle are separated into different areas of the lake. When ammonium diffuses from anoxic layers, nitrifying bacteria use that ammonium to produce nitrate at the border between oxic and anoxic water. [7] When nitrate and nitrous oxide diffuse into the anoxic layers, denitrification occurs. [7] Decomposition also occurs within the anoxic layer, which releases ammonium through sulphate reduction. [7]
Key Microorganisms
Antarctic lakes do not have large food chains, as no fish are present, resulting in microbes dominating the system. Cite error: Closing </ref> missing for <ref> tag Some main viruses in these communities are single stranded DNA (ssDNA) viruses, which infect eukaryotes, and double stranded DNA (dsDNA) viruses, which infect algae. [8] However, there is a large diversity of viruses in these lakes, many of which that have yet to be identified. [8]
Current Research
1 Scientists are have recently researched the microbial diversity of a sediment sample from Lake Hodgson.[9] It was found that 77% of the microorganism diversity could be identified with previously found microbes, while 23% could not be recognized.[10] This indicates that a large number of microbes still remain unknown to scientists. Further research is necessary to continue to reveal more information on the diversity of microbes, and how they continue to live in the extreme Antarctic Lake conditions. [10]
2 Research in Deep Lake has demonstrated that horizontal gene transfer occurs quite frequently between microorganisms. [11] Large DNA segments are exchanged between different classes of microorganisms, leading to evolution.[11] This allows the microorganisms to avoid competition for resources, as the exchanged DNA helps with niche adaptation.[11]
References
- ↑ 1.0 1.1 1.2 1.3 Laybourn-Parry, J. (2009). Microbiology. No place too cold. Science (New York, N.Y.), 324(5934), 1521.
- ↑ 2.0 2.1 Laybourn-Parry, J. (2002). Survival mechanisms in antarctic lakes. Philosophical Transactions of the Royal Society of London.Series B: Biological Sciences, 357(1423), 863-869
- ↑ 3.0 3.1 Priscu, J. C., Tabacco, I., Kennicutt, M. C., Bell, R. E., Bulat, S. A., Ellis-Evans, J. C., and Siegert, M. J. (2005).
- ↑ 4.0 4.1 4.2 4.3 4.4 Cowan, D. A., and Tow, L. A. (2004). Endangered antarctic environments. Annual Review of Microbiology, 58(1), 649-690.
- ↑ Burton, H. R. (1981). 24. chemistry, physics and evolution of antarctic saline lakes: A review. Hydrobiologia, 81-82(1), 339-362.
- ↑ Wharton, J.,R A., McKay, C. P., Simmons, J.,G M., and Parker, B. C. (1986). Oxygen budget of a perennially ice-covered antarctic lake. Limnology and Oceanography, 31(2), 437.
- ↑ 7.0 7.1 7.2 Howard-Williams, C., and Hawes, I. (2007). Ecological processes in antarctic inland waters: Interactions between physical processes and the nitrogen cycle. Antarctic Science, 19(2), 205-217.
- ↑ 8.0 8.1 Cite error: Invalid
<ref>tag; no text was provided for refs namedLopez - ↑ Pearce, D.A., Hodgson, D.A., Thorne, M.A.S., Burns, G., and Cockell, C.S. (2013). Preliminary analysis of life within a former subglacial lake sediment in antarctica. Diversity, 5(3), 680-702.
- ↑ 10.0 10.1 Cite error: Invalid
<ref>tag; no text was provided for refs namedPearce - ↑ 11.0 11.1 11.2 Demaere, M. Z., Woyke, T., Kyrpides, N. C., Tringe, S. G., Cavicchioli, R., Williams, T. J., and Davenport, K. W. (2013). High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated antarctic lake. Proceedings of the National Academy of Sciences of the United States of America, 110(42), 16939.
