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Assignment #5

[edit]

Microbial symbiosis is the long-term interaction between two organisms. It affects the ecosystem, and it is important to the living of all organisms. Based on where the symbiont is found, microbial symbiosis is categorized into two types: endosymbiosis and ectosymbiosis, and they are either mutualistic, commensalistic, or parasitic.

Microbial symbiosis has great impacts on the environment, especially biogeochemical cycles like nitrogen cycle.[1] Endosymbiosis is the living of one organism within another organism's cells, and the symbiotic relationship between Rhizobium and legumes is a typical example. Rhizobium infects root cells of legumes, forming a new compartment: root nodule. Rhizobium then differentiate into endosymbiotic bacteroid that performs nitrogen fixation to help plants grow because plants cannot use atmospheric nitrogen as a nitrogen source.[2] Ammonium, which is a fertilizer, is also produced during nitrogen fixation. When leguminous plants decompose, non-legume crops can use those ammonium as their nitrogen source.

Ectosymbiosis is the living of the symbiont on the body surface of the host. One example is the microbes that live on the surface of cow's rumen. They are essential to cows because microbial enzymes can breakdown cellulose, while mammalian enzymes cannot. Cows can only use the fermentation waste products produced by anaerobic rumen microbes for metabolic processes such as energy conservation and synthesis of nutrients.[3] However, methane is a greenhouse gas which affects the global warming, and it is produced by methogenic Archaea in the rumen.[4]

  1. ^ Lodwig, E. M.; Hosie, A. H. F.; Bourdès, A.; Findlay, K.; Allaway, D.; Karunakaran, R.; Downie, J. A.; Poole, P. S. (17 April 2003). "Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis". Nature. 422 (6933): 722–726. doi:10.1038/nature01527.
  2. ^ Mylona, P. (1 July 1995). "Symbiotic Nitrogen Fixation". THE PLANT CELL ONLINE. 7 (7): 869–885. doi:10.1105/tpc.7.7.869.
  3. ^ Lourenço, M.; Ramos-Morales, E.; Wallace, R. J. (23 March 2010). "The role of microbes in rumen lipolysis and biohydrogenation and their manipulation". animal. 4 (07): 1008–1023. doi:10.1017/S175173111000042X.
  4. ^ ELLIS, J. L.; DIJKSTRA, J.; KEBREAB, E.; BANNINK, A.; ODONGO, N. E.; McBRIDE, B. W.; FRANCE, J. (26 March 2008). "Aspects of rumen microbiology central to mechanistic modelling of methane production in cattle". The Journal of Agricultural Science. 146 (02). doi:10.1017/S0021859608007752. {{cite journal}}: no-break space character in |first1= at position 3 (help); no-break space character in |first5= at position 3 (help); no-break space character in |first6= at position 3 (help)

Charlene yjy (talk) 00:49, 20 November 2017 (UTC)

Assignment #3: Original - Microbial ecology ("Symbiosis" section)

[edit]

Microbes, especially bacteria, often engage in symbiotic relationships (either positive or negative) with other organisms, and these relationships affect the ecosystem. One example of these fundamental symbioses are chloroplasts, which allow eukaryotes to conduct photosynthesis. Chloroplasts are considered to be endosymbiotic cyanobacteria, a group of bacteria that are thought to be the origins of aerobic photosynthesis. Some theories state that this invention coincides with a major shift in the early earth's atmosphere, from a reducing atmosphere to an oxygen-rich atmosphere. Some theories go as far as saying that this shift in the balance of gases might have triggered a global ice-age known as the Snowball Earth [citation needed].


Assignment #3: Edit - Microbial ecology ("Symbiosis" section)

[edit]

Microbial symbiosis is important to the living of all creatures, and it has an impact to the environment.

There are two types of symbiosis: ectosymbiosis and endosymbiosis. Rumen is an example of ectosymbiosis, and microbes in the rumen are essential to cows' lives. Microbial enzymes can breakdown cellulose, while mammalian enzymes cannot. The end product, glucose, is not directly absorbed by the cow. Instead, anaerobic rumen microbes ferment glucose, and the fermentation waste products, for example, volatile fatty acids, are absorbed into cows' blood, and these waste products are the main sources of energy and electrons.[1] However, methane as a waste product from methogenic Archaea in the rumen is a greenhouse gas, which affects the global warming.[2]

Microbial symbiosis also has great impact on the environment, especially for biogeochemical cycles like nitrogen cycle.[3] An important endosymbiosis for nitrogen cycle is the symbiosis between Rhizobium and legumes. Plants need nitrogen for growth, but they cannot use atmospheric nitrogen as an nitrogen source. While bacteria can fix atmospheric nitrogen, but they cannot produce sufficient energy for nitrogen fixation. Legume roots secrete a chemical which attracts Rhizobium, then they form a new compartment: root nodule. Rhizobium then differentiate into endosymbiotic bacteroid that performs N-fixation.[4] With a plant-derived membrane, bacteroid and legumes cooperate to synthesize leghemoglobin that stores oxygen, so that nitrogenase can carry out nitrogen fixation and produce ammonium.[5] Ammonium is a fertilizer, and as leguminous plants decompose, non-legume crops can use ammonium as well.

  1. ^ Lourenço, M.; Ramos-Morales, E.; Wallace, R. J. (23 March 2010). "The role of microbes in rumen lipolysis and biohydrogenation and their manipulation". animal. 4 (07): 1008–1023. doi:10.1017/S175173111000042X.
  2. ^ ELLIS, J. L.; DIJKSTRA, J.; KEBREAB, E.; BANNINK, A.; ODONGO, N. E.; McBRIDE, B. W.; FRANCE, J. (26 March 2008). "Aspects of rumen microbiology central to mechanistic modelling of methane production in cattle". The Journal of Agricultural Science. 146 (02). doi:10.1017/S0021859608007752.
  3. ^ Lodwig, E. M.; Hosie, A. H. F.; Bourdès, A.; Findlay, K.; Allaway, D.; Karunakaran, R.; Downie, J. A.; Poole, P. S. (17 April 2003). "Amino-acid cycling drives nitrogen fixation in the legume–Rhizobium symbiosis". Nature. 422 (6933): 722–726. doi:10.1038/nature01527.
  4. ^ Mylona, P. (1 July 1995). "Symbiotic Nitrogen Fixation". THE PLANT CELL ONLINE. 7 (7): 869–885. doi:10.1105/tpc.7.7.869.
  5. ^ Sainz, Martha; Calvo-Begueria, Laura; Pérez-Rontomé, Carmen; Wienkoop, Stefanie; Abián, Joaquín; Staudinger, Christiana; Bartesaghi, Silvina; Radi, Rafael; Becana, Manuel (March 2015). "Leghemoglobin is nitrated in functional legume nodules in a tyrosine residue within the heme cavity by a nitrite/peroxide-dependent mechanism". The Plant Journal. 81 (5): 723–735. doi:10.1111/tpj.12762.

Charlene yjy (talk) 02:49, 8 October 2017 (UTC)

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