Termite gut: Difference between revisions
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===Do the microbes carry out any metabolism that affects their environment?=== | ===Do the microbes carry out any metabolism that affects their environment?=== | ||
1. Nitrogen fixation and recycling of uric acid nitrogen | |||
N₂ fixation is one of the crucial aspects of termite gut symbiosis, because termites feed on the nitrogen poor environment. The Nitrogen fixing bacteria such as Citrobacter freundii, Enterobbacter agglomerans, and Spirochaeta possess nitrogenase which reduces N₂ to 2NH₃, providing nitrogenous compounds that TG1 cannot synthesis. They play significant role in converting stable atmospheric nitrogen into something that host protists can uptake in order to supply the nitrogen need. Also, because the supply is so scarce, most of the nitrogen is recycled through the uric acid recycling to minimize the nitrogen loss. Generally, the required nitrogen fixation is low comparing to the high concentration in the termite due to the recycling of the uric acid (7). | |||
2 .Acetogenesis/Methanogenesis | |||
Both H₂/CO₂ acetogenisis and methanogenesis are anaerobic metabolism pathway that utilizes H₂ plus CO₂ generated by host protists during cellulose fermentation to synthesize acetate and methane, respectively. Prokaryotes associated with protists as symbionts are key microbes that are responsible for mediating these biosynthesis. Treponema acts as acetogens and carrys out acetogenesis by reducing CO₂: 4H₂ + 2CO₂ -> CH₃COOH + 2H₂O. Methanobrevibacter takes more of methanogenic role and also uses H₂ as its reducing agent for methane production: 4H₂ + CO₂ -> CH₄ + 2H₂O (3). Since the termite only can absorb acetate as its energy source, acetogenesis dominates methanogenesis in the termite gut to reduce energy loss as much as possible. Thus, only 1% of the carbon generated by microbes is lost in form of CH₄ and the rest 99% C source are emitted as CO₂ (3). But it appears to be that even small amount methane emitted by archaea-mediating metanogenesis are considered to be significant atmospheric methane source. | |||
3. Cellulose degradation | |||
Protists reside in the termite gut ingest wood particles in the form of cellulose and degrade it within their cells. Cellulolytic protists known as Trichonympha and mixotricha produce cellulases and various glycolytic enzymes that can break down cellulose and convert it into an intermediate product, malate (2). In addition, they carry specific anaerobic energy- generating organelle, hydrogenosome, where transferred malate from the cytoplasm is further fermented to produce CO₂, H₂, and acetate with the help of hydrogenase enzyme. During this fermentation process, ATP is also produced in the way and stored as energy available for both microbes and termite (2). | |||
==Current Research== | ==Current Research== | ||
Revision as of 05:36, 30 August 2008
Introduction
Description of Niche
Location
Physical Conditions
What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.
Influence by Adjacent Communities (if any)
Is your niche close to another niche or influenced by another community of organisms?
Conditions under which the environment changes
Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.
Who lives there?
Which microbes are present?
Termite gut exhibits one of the most complex microbial communities, consisting of diverse microorganisms from all three domains of life: Bacteria, Archaea, and Eukarya. By extracting DNA from the gut and comparing sequences of 16S rRNA genes with databases of rRNA sequences, predominant microorganisms in the gut community has been identified as well as their funcitons in the termite gut(1):
Do the microbes that are present interact with each other?
Interaction between the microbes in the termite gut is highly mutual, usually beneficial for both microbes.
Prokaryotes are closely associated with protists as symbionts, either attached to the cell surfaces or live within the cytoplasm or nucleus of the protists. For instance, Treponema spirochete bacteria are attached to the special bracket-like structures on the plasma membrane of mixotricha and contributes to the movement of the host protist known as “motility symbiosis”(3). Treponema also benefits by living on and within the protist, easilly accessible to nutrients H₂ and CO₂ produced by mixotricha and utilize them to synthesize acetate and obtain energy for their own growth as well (5).
Another mutual relationship shown between Methanobrevibacter and parabasalids protist, H₂ plus CO₂ produced by protists also can be used by methanogens as energy source but they form methane,CH₄ in this case. Successful elimination of produced H₂ by endosymbiont’s H₂ evolution activity enables the protists to maintain optimal pH and stimulate its decomposition activity (4). These two groups of microorganism interact and work together to digest cellulose and enhance the cellulose fermentation.
Although most of the microbes act mutually, there is one exception between the relationship of methanogens and acetogens. Both take up H₂ and CO₂ as their substrates, thus they are likely to be in a compete relationship. Acetogenesis dominates methanogenesis from the same substrate, H₂ plus CO₂, because acetogenesis requires less energy loss of the termite by absorbing acetates but not methane as the energy source.(4)
Do the microbes change their environment?
The genus Treponema contains motile spirochetes that are embedded in the host’s cell membrane. They work as ectobionts to provide locomotion of the host cell by moving synchronizedly. Such relationship is known as the motility symbiosis (8).
Termites are on the nitrogen poor diet. Hence, the functional group of nitrogen fixers is essential to supplement a sufficient amount of nitrogen to the host protists. Treponema, Citobacter, Enterobacter, and Spirochaeta are some of the responsible nitrogen fixers. These microbes convert N2 from the atmosphere to NH3 and fix ~60% of the nitrogen supply of the host (7).
In the protest Pseudotrichonympha grassii, there are two gens enconding hydrogenosomal iron-hydrogenases. Two iron-hydrogenases are responsible for retaining optimal pH within the hydrogenosome in the protest cell. These enzymes catalyze H2 evolution instead of H2 uptake (6).
Do the microbes carry out any metabolism that affects their environment?
1. Nitrogen fixation and recycling of uric acid nitrogen N₂ fixation is one of the crucial aspects of termite gut symbiosis, because termites feed on the nitrogen poor environment. The Nitrogen fixing bacteria such as Citrobacter freundii, Enterobbacter agglomerans, and Spirochaeta possess nitrogenase which reduces N₂ to 2NH₃, providing nitrogenous compounds that TG1 cannot synthesis. They play significant role in converting stable atmospheric nitrogen into something that host protists can uptake in order to supply the nitrogen need. Also, because the supply is so scarce, most of the nitrogen is recycled through the uric acid recycling to minimize the nitrogen loss. Generally, the required nitrogen fixation is low comparing to the high concentration in the termite due to the recycling of the uric acid (7).
2 .Acetogenesis/Methanogenesis
Both H₂/CO₂ acetogenisis and methanogenesis are anaerobic metabolism pathway that utilizes H₂ plus CO₂ generated by host protists during cellulose fermentation to synthesize acetate and methane, respectively. Prokaryotes associated with protists as symbionts are key microbes that are responsible for mediating these biosynthesis. Treponema acts as acetogens and carrys out acetogenesis by reducing CO₂: 4H₂ + 2CO₂ -> CH₃COOH + 2H₂O. Methanobrevibacter takes more of methanogenic role and also uses H₂ as its reducing agent for methane production: 4H₂ + CO₂ -> CH₄ + 2H₂O (3). Since the termite only can absorb acetate as its energy source, acetogenesis dominates methanogenesis in the termite gut to reduce energy loss as much as possible. Thus, only 1% of the carbon generated by microbes is lost in form of CH₄ and the rest 99% C source are emitted as CO₂ (3). But it appears to be that even small amount methane emitted by archaea-mediating metanogenesis are considered to be significant atmospheric methane source.
3. Cellulose degradation
Protists reside in the termite gut ingest wood particles in the form of cellulose and degrade it within their cells. Cellulolytic protists known as Trichonympha and mixotricha produce cellulases and various glycolytic enzymes that can break down cellulose and convert it into an intermediate product, malate (2). In addition, they carry specific anaerobic energy- generating organelle, hydrogenosome, where transferred malate from the cytoplasm is further fermented to produce CO₂, H₂, and acetate with the help of hydrogenase enzyme. During this fermentation process, ATP is also produced in the way and stored as energy available for both microbes and termite (2).
Current Research
Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)
References
Edited by [insert your names here!], students of Rachel Larsen
