Trichonympha

Definition, Classification and Characteristics


Definition:  What is Trichonympha?



Trichonympha is a genus consisting of parabasalid protists found in the hindgut of lower termite species as well as cockroach that feed on wood. As such, they have a symbiotic relationship with their hosts in that they help break down cellulose present in the wood while the host provides a favorable living environment in which they reside.

Members of the genus Trichonympha are characterized by numerous flagella on their surface which makes them some of the most visually striking single-celled organisms

Initially, it was thought that members of the genus Trichonympha were unable to digest cellulose in the absence of certain symbiotic bacteria, however, new findings from various studies showed that they were capable of digesting cellulose even in the absence of these bacteria.

Some studies have suggested that a symbiotic relationship also exists between the flagellates (Trichonympha species) and some bacteria species found in this environment.


 

Some of the most common species of this genus include:

  • T. grandis
  • T. agilis Leidy
  • T. burlesquei 
  • T. campanula
  • T. postcylindrica


Classification of the genus Trichonympha


Domain: Eukaryota - As a member of the domain Eukaryota, members of the genus trichonympha are have membrane-bound organelles including a nucleus that is enclosed within a nuclear membrane

Phylum: Metamonada - This phylum is composed of a large group of anaerobic flagellates that have formed a symbiotic relationship with various animals. However, some of these organisms have been shown to be pathogenic in nature and can cause diseases.

Class: Parabasalia - Members of the class parabasalia fall under the super-group excavata. They are single-celled organisms that use flagella for motility and tend to form symbiotic relationships with various animals. 

Order: Hypermastigida - The Order Hypermastigida is composed of heavily flagellated protozoa typically found in the gut of termites and wood roaches (they have a symbiotic relationship with these hosts). 

Family: Trichonymphidae - Members of this family are characterized by a short and broad body as well as relatively short flagella. They have a ribbon-shaped body as well as a putative nucleus that is located in the upper third part of the body. They are typically found in the gut of termites (as well as cockroaches that feed on wood). 

* Members of the genus Trichonympha also fall under the super-group Excavata which consists of many single-celled organisms under the domain Eukaryota. This group also consists of both free-living and parasite organisms that are spread in various habitats across the globe. 



Life Cycle


Unlike various microorganisms that depend on two hosts to complete their life cycle, the complete life cycle of Trichonympha species takes place in the gut of their hosts. 



Sexual Reproduction


For many of the flagellates found in their respective hosts, sexual reproduction is influenced by the molting hormone of the host. Therefore, fertilization among these organisms is limited. For Trichonympha species, sexual reproduction has been shown to start about 5 days before molting takes place. 

During sexual reproduction, gamonts of the organisms develop a cyst. This is characterized by the resorption of the extracellular organelles with only a few of the organelles within the cells remaining intact (centrioles, nuclear cap etc).

Gamete formation occurs within the cyst and can take about 5 days before ecdysis occurs. During this period, the cyst is particularly important given that it protects the organisms during molting. Here, this resistant form of the flagellate is held in place within the gut lining (old lining) of the host until a new lining is formed. 

Within the cyst, centrioles start moving to the pole opposites of the cell with a spindle fiber-forming between them. This allows for nuclear division to take place thus forming two daughter nuclei. A nuclear cap then develops around each daughter nucleus. This is followed by flagella elongation as well as the formation of new parabasal bodies and ultimately cytoplasmic division.

Eventually, the new cells (gametes) leave the cyst and undergo further development. 

During development, one of the gametes (the egg) develops granules that attract other gametes (sperm gametes) for fertilization to take place. Here, the male gamete attaches itself and penetrates the female cone while allows for gamete fusion. This results in the formation of a zygote that in turn undergoes meiosis (meiosis 1 and meiosis II) to produce 4 haploid cells.


Asexual Reproduction


Asexual reproduction, which is the most common mode of reproduction among trichonympha species, occurs through binary fission. This occurs through a number of stages that ultimately divide the cell into two new daughter cells (mitosis).

Division starts with the dividing of the nucleus (which is two thirds away from the anterior part of the cell known as the rostrum). This is followed by the division of the cytoplasm as the cell starts dividing at the rostrum. Ultimately, the cell divides into two new cells that develop and grow in size with increased production of the cytoplasm. 


In asexual reproduction, centrioles give rise to the flagella and parabasal body. 


Morphology/Structure of Trichonympha Species


With regards to morphology, Trichonympha species have been shown to be large in size measuring between 30 and 110um um in length and 21 to 90um in width.

Apart from a rounded, bell-shaped body, members of the genus Trichonympha are also characterized by numerous flagella which can be as many as ten thousand or more. These allow the flagellate to navigate through the highly viscous environment in the hindgut of the termite (or cockroach that feed on wood). 

The anterior part of the cell (known as the rostral cap) is protruded and is therefore not as broad as the posterior part of the cell. Microscopic observation of the cell has also revealed the cell to consist of both an ectoplasm and endoplasm (with most of the cell organelles being contained within the endoplasm). 

* Unlike most eukaryotic cells, Trichonympha species do not have mitochondria.

* Flagella do not cover the rostra cap of trichonympha cells.

Apart from the high number of flagella, Trichonympha species are also characterized by an exceptionally long basal body. However, they also vary in length depending on where they are located.

Whereas basal bodies that are located in the anterior region of the cell tend to be longer, those located at the posterior part of the cell have been shown to be shorter. Which formation of these bodies is yet to be fully understood, studies have shown that they are responsible for flagella production.


Trichonympha and Bacteria


A close examination of Trichonympha species revealed that they harbor a rod-shaped bacteria (e.g. Candidatus Endomicrobium trichonymphae and Candidatus Desulfovibrio trichonymphae).

While some of the bacteria were found to live within the protist (as endosymbionts), others were found to be attached to the cell at their posterior end. However, they were found to be absent between the flagella given their closely spaced nature that does not allow for bacteria attachment. 

While some bacteria are capable of digesting cellulose and thus contribute to its digestion in the gut of termites (as well as cockroach), their mutual relationship with Trichonympha has been shown to involve nitrogen fixation as well as the provision of nitrogenous compounds required by the organisms. 

In this environment, bacteria are capable of nitrogen fixation as well as producing nitrogenous compounds that are not produced during cellulose digestion by Trichonympha species. 

Here, Trichonympha species benefit from this association by using the nutrients produced by the bacteria. This relationship, however, is regulated by the requirements of the protist. That is to say that for species that need more of these nutrients/compounds, the surface of bacterial attachment is greater as compared to those with fewer requirements. 


Read more about Bacteria here.



Trichonympha and Termites 
(Symbiotic Relationship)


Unlike the relationship between Trichonympha species and bacteria where some of the bacteria are attached to the protists externally, Trichonympha species are exclusively found in the hindgut of termites and some cockroaches. 

While termites feed on wood as one of their main sources of nutrition, they lack the enzymes required to digest and breakdown cellulose present in this food source. For this reason, they are dependent on Trichonympha species that are capable of breaking down this compound to its constituents that are useful to the protists. 

In their salivary glands, termites as well as cockroaches that feed on wood have been shown to contain enzymes that initiate the digestion of cellulose in plants/wood. However, this process is not completed given that the enzymes are incapable of fully digesting cellulose. 

When it comes to Trichonympha species, a variety of bacteria, as well as enzymes present in their posterior/bulbous end, are able to break down the molecule into sugar that can then be used by both the flagellate and the termite. 

Here, glycoside hydrolases is one of the most important enzymes used to break down the polysaccharide. It achieves this by breaking down the glycosidic bonds of cellulose and ultimately releases metabolizable products (simple sugars) that can be used for energy production.

Given that a majority of termites feed on wood/plant material as their main source of nutrition, they would not be able to feed on these sources without the presence of symbiotic protists. 

While they (termites) have a number of bacteria that are also capable of breaking down the molecule (cellulose), Trichonympha species present in the gut of these insects play a major role in this activity and thus cellulose digestion would be significantly (some termites can starve to death) affected in their absence. 

The interdependence between the termites and Trichonympha species is also beneficial to Trichonympha species. Conditions inside the hindgut of termites are favorable and support the life cycle of Trichonympha species. 

As a result, the flagellates would die outside the termite as has been shown to be the case during molting. Here, according to studies, flagellates that remain attached to the old lining of the insect are unable to survive while those found in the new lining of termites (after molting) continue reproducing. 

* Flagellates, like Trichonympha, are highly sensitive to changing conditions in their environment. For this reason, cysts are formed during host molting to protect them from these changes. 


* While termites cause significant damage to timber and homes made of wood, being some of the most pervasive insects on earth, they play an important ecological role in that they help in the breakdown of wood and other plant fiber which contributes to soil fertility and nutrient recycling.  



Disease


Typically, Trichonympha species (as well as termites) do not cause diseases in animals or plants. However, given that they help in the breakdown of cellulose in wood and plant material, they, along with their hosts, have been shown to contribute to asthma attacks. 

By feeding on wood, termites end up contributing to dust in homes which can aggravate asthma and allergic reactions for some people. As well, termite droppings have been shown to result in allergic reactions for some people which is why calling pest control is suggested in such cases. 



Microscopy


Trichonympha species can be observed under the compound microscope using a saline solution (isotonic). 

Requirements


Procedure

· Using a pipette, place a drop of isotonic saline solution on to a glass slide or a small Petri dish


· Using the forceps, carefully hold the termite by its head and place it on the drop of saline - Here, the slide/Petri dish may be placed on a stereomicroscope in order to carefully remove the gut


· By manipulating a dissecting needle, remove the gut of the termite (under the stereomicroscope)


· Carefully pull the gut apart to small pieces


· Transfer the pieces of gut onto a glass slide with a drop of the saline solution (or simply use the original slide used for dissection)


· Cover the sample (gut pieces) with a coverslip and observe the slide under the compound microscope - Start with low power and switch to high power to get a clear view of the flagellate


Observation


When viewed under the microscope, Trichonympha species are characterized by a high number of flagella on their surface. The body may be bell-shaped with a protruding anterior and broad posterior. 



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References


Christine A. Nalepa. (2017). What Kills the Hindgut Flagellates of Lower Termites

during the Host Molting Cycle?

James W. Perry, David Morton, and Joy B. Perry. (2012). Laboratory Manual for Non-Majors Biology.

Karl Gottlieb Grell. (1956). Protozoology. 

Kevin J. Carpenter, Lawrence Chow and Patrick J. Keeling. (2009). Morphology, Phylogeny, and Diversity of Trichonympha (Parabasalia: Hypermastigida) of the Wood Feeding Cockroach Cryptocercus punctulatus. 

Nicholas P. Money. (2014). Microbiology: A Very Short Introduction

V. B. Rastogi, B. Kishore. (1997). A Complete Course in ISC Biology.

Vittorio Boscaro. (2017). Molecular characterization and phylogeny of four new species of the genus Trichonympha (Parabasalia, Trichonymphea) from lower termite hindguts. International Journal of Systematic and Evolutionary Microbiology. 


Links 

https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.054874-0

https://discoverbiology101.files.wordpress.com/2014/09/termites-and-trichonympha.pdf


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