Nematocida parisii: Difference between revisions

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==Introduction to Microsporidia==
==Introduction to Microsporidia==
[[Image: He1.png|thumb|300px|right|The process of polar tube eversion during spore germination in microsporidia.
<br>Microsporidia are a phylum of eukaryotic, intracellular, spore-forming parasites [1]. Fungi are currently considered the closest relative to this phylum, but it is still being debated whether or not they should be categorized as Fungi [1,2, 3]. Microsporidia are able to use vertebrates as well as invertebrates as hosts. They are most prevalent in arthropods and fish [1]. The life cycles of microsporidia vary between each species, but all species have at least one intracellular and extracellular spore stage [3]. Microsporidian spores range in size from 1 um to 40 um and also vary in shape from spherical to rod-shaped to crescent-shaped [1]. However, a majority of the species has an ovoid spore. Microsporidia are able to survive outside of their hosts as spores [6]. Microsporidian spores are characterized by its thick chitinous cell wall surround the cell membrane and the presence of a polar filament inside the spore [3]. Polar filaments are tubes located within the spore, attached to the apex of the spore by an anchoring disk [1].  These polar filaments are an essential component to allow for spore germination and infection of the host cell.<br> [[Image: He1.png|thumb|300px|right|The process of polar tube eversion during spore germination in microsporidia.
<br>A) Shows a dormant spore containing a polar filament (black), nucleus (gray), polaroplast and posterior vacuole.
<br>A) Shows a dormant spore containing a polar filament (black), nucleus (gray), polaroplast and posterior vacuole.
<br>B) The posterior vacuole swells with water and ruptures the anchoring disk, allowing the polar filament to emerge through through spore cell wall.
<br>B) The posterior vacuole swells with water and ruptures the anchoring disk, allowing the polar filament to emerge through through spore cell wall.
Line 7: Line 7:
<br>E) Sporoplasm is moving through the polar tube.
<br>E) Sporoplasm is moving through the polar tube.
<br>F) Entire sporoplasm emerges from the polar tube while bound to the new membrane<br><br> Image source: http://www.annualreviews.org/doi/pdf/10.1146/annurev.micro.56.012302.160854 [1]]]
<br>F) Entire sporoplasm emerges from the polar tube while bound to the new membrane<br><br> Image source: http://www.annualreviews.org/doi/pdf/10.1146/annurev.micro.56.012302.160854 [1]]]
<br>Microsporidia are a phylum of eukaryotic, intracellular, spore-forming parasites [1]. Fungi are currently considered the closest relative to this phylum, but it is still being debated whether or not they should be categorized as Fungi [1,2, 3]. Microsporidia are able to use vertebrates as well as invertebrates as hosts. They are most prevalent in arthropods and fish [1]. The life cycles of microsporidia vary between each species, but all species have at least one intracellular and extracellular spore stage [3]. Microsporidian spores range in size from 1 um to 40 um and also vary in shape from spherical to rod-shaped to crescent-shaped [1]. However, a majority of the species has an ovoid spore. Microsporidia are able to survive outside of their hosts as spores [6]. Microsporidian spores are characterized by its thick chitinous cell wall surround the cell membrane and the presence of a polar filament inside the spore [3]. Polar filaments are tubes located within the spore, attached to the apex of the spore by an anchoring disk [1].  These polar filaments are an essential component to allow for spore germination and infection of the host cell.<br>
<br>Spore germination in microsporidian spores occurs in several phases: activation, increase in intrasporal osmotic pressure, eversion of the polar tube, and passage of sporoplasm through the polar tube [2]. Microsporidia has to be activated by an environmental trigger such as change in pH, presence of ions, or ultraviolet radiation exposure. Since microsporidia live in a wide range of hosts, each species requires a different activation condition. In response to the activation, all microsporidia respond by increasing flow of water into spore, increasing intrasporal osmotic pressure and swelling the polaroplast [2]. The pressure build-up within the spore becomes the driving force of germination as it forces the eversion of the polar tube [1]. In eversion, the discharging polar filament breaks through the thinnest portion of the spore cell wall (Figure 1B), where it serves as a polar tube (Figure 1D). The polar tube is used as a bridge to siphon the sporoplasm out of the spore and into its host cell [2]. However, it has yet to be determined how exactly the polar tube or sporoplasm interacts with the host cell’s membrane. It is a predicted possibility that the polar tube launches and pierces the cell membrane of a nearby host cell and injects the sporoplasm, allowing it to avoid all extracellular defenses [1,2,7].<br>
<br>Spore germination in microsporidian spores occurs in several phases: activation, increase in intrasporal osmotic pressure, eversion of the polar tube, and passage of sporoplasm through the polar tube [2]. Microsporidia has to be activated by an environmental trigger such as change in pH, presence of ions, or ultraviolet radiation exposure. Since microsporidia live in a wide range of hosts, each species requires a different activation condition. In response to the activation, all microsporidia respond by increasing flow of water into spore, increasing intrasporal osmotic pressure and swelling the polaroplast [2]. The pressure build-up within the spore becomes the driving force of germination as it forces the eversion of the polar tube [1]. In eversion, the discharging polar filament breaks through the thinnest portion of the spore cell wall (Figure 1B), where it serves as a polar tube (Figure 1D). The polar tube is used as a bridge to siphon the sporoplasm out of the spore and into its host cell [2]. However, it has yet to be determined how exactly the polar tube or sporoplasm interacts with the host cell’s membrane. It is a predicted possibility that the polar tube launches and pierces the cell membrane of a nearby host cell and injects the sporoplasm, allowing it to avoid all extracellular defenses [1,2,7].<br>
<br>Once the sporoplasm of the microsporidia spore is in the host cell, it replicates in a form without a cell wall called meront [6]. Meronts differentiate and develops into the spore form. Once the meronts complete development, they will begin producing more spores, which will be used to infest other host cells [5].
<br>Once the sporoplasm of the microsporidia spore is in the host cell, it replicates in a form without a cell wall called meront [6]. Meronts differentiate and develops into the spore form. Once the meronts complete development, they will begin producing more spores, which will be used to infest other host cells [5].

Revision as of 04:46, 20 April 2014

Introduction to Microsporidia


Microsporidia are a phylum of eukaryotic, intracellular, spore-forming parasites [1]. Fungi are currently considered the closest relative to this phylum, but it is still being debated whether or not they should be categorized as Fungi [1,2, 3]. Microsporidia are able to use vertebrates as well as invertebrates as hosts. They are most prevalent in arthropods and fish [1]. The life cycles of microsporidia vary between each species, but all species have at least one intracellular and extracellular spore stage [3]. Microsporidian spores range in size from 1 um to 40 um and also vary in shape from spherical to rod-shaped to crescent-shaped [1]. However, a majority of the species has an ovoid spore. Microsporidia are able to survive outside of their hosts as spores [6]. Microsporidian spores are characterized by its thick chitinous cell wall surround the cell membrane and the presence of a polar filament inside the spore [3]. Polar filaments are tubes located within the spore, attached to the apex of the spore by an anchoring disk [1]. These polar filaments are an essential component to allow for spore germination and infection of the host cell.

The process of polar tube eversion during spore germination in microsporidia.
A) Shows a dormant spore containing a polar filament (black), nucleus (gray), polaroplast and posterior vacuole.
B) The posterior vacuole swells with water and ruptures the anchoring disk, allowing the polar filament to emerge through through spore cell wall.
C) Polar filament continues to to outward and evert.
D) Polar filament is fully everted and becomes a polar tube. Sporoplasm is squeezed into the polar tube.
E) Sporoplasm is moving through the polar tube.
F) Entire sporoplasm emerges from the polar tube while bound to the new membrane

Image source: http://www.annualreviews.org/doi/pdf/10.1146/annurev.micro.56.012302.160854 [1]


Spore germination in microsporidian spores occurs in several phases: activation, increase in intrasporal osmotic pressure, eversion of the polar tube, and passage of sporoplasm through the polar tube [2]. Microsporidia has to be activated by an environmental trigger such as change in pH, presence of ions, or ultraviolet radiation exposure. Since microsporidia live in a wide range of hosts, each species requires a different activation condition. In response to the activation, all microsporidia respond by increasing flow of water into spore, increasing intrasporal osmotic pressure and swelling the polaroplast [2]. The pressure build-up within the spore becomes the driving force of germination as it forces the eversion of the polar tube [1]. In eversion, the discharging polar filament breaks through the thinnest portion of the spore cell wall (Figure 1B), where it serves as a polar tube (Figure 1D). The polar tube is used as a bridge to siphon the sporoplasm out of the spore and into its host cell [2]. However, it has yet to be determined how exactly the polar tube or sporoplasm interacts with the host cell’s membrane. It is a predicted possibility that the polar tube launches and pierces the cell membrane of a nearby host cell and injects the sporoplasm, allowing it to avoid all extracellular defenses [1,2,7].

Once the sporoplasm of the microsporidia spore is in the host cell, it replicates in a form without a cell wall called meront [6]. Meronts differentiate and develops into the spore form. Once the meronts complete development, they will begin producing more spores, which will be used to infest other host cells [5].

Microsporidia have mitochondria, which are used for their metabolism. However, they do not have electron transfer chains, oxidative phosphorylation, and the tricarboxylic acid (TCA) cycle [1]. Instead of these pathways, microsporidia break down glucose with glycolysis and followed by substrate-level phosphorylation. The resulting pyruvate from glycolysis is decarboxylated by either pyruvate dehydrogenase complex (PDHC) or the enzyme, pyruvate:ferredoxin oxidoreductase in anaerobic microsporidia [1]. Electrons are removed from pyruvate and placed on ferredoxin, which is later transferred to NADH and then to an organic terminal electron acceptor. The lack of TCA cycle induces a requirement for ATP, so the microsporidia also conduct fermentation to synthesis ATP and also had enzymes found in pentose-phosphate pathway (PPP) [1].

Background on Nematocida parisii

Pathogenesis of various microsporidia including Nematocida parisii.

Image source: http://www.plosbiology.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pbio.1000005&representation=PDF [3]


Caenorhabditis elegans are model organisms for many different fields of biology, ranging from behavioral to neurobiological research. Over time, C. elegans has become a more and more popular host for studying pathogenesis as a result of the discovery of intracellular pathogens. In Franconville, France, a community outside of Paris, a wild-caught C. elegans isolated from a compost bin was discovered to have the presence of microbial rod-shaped cells in its intestinal cells [4]. The rod-shaped cells were Nematocida parisii, an intracellular microsporidium that invade intestinal cells of C. elegans (Figure 2). N. parisii became of interest in the research community because it was the first pathogen isolated directly from a wild-caught C. elegans and it was the first pathogen that invaded and lived in C. elegans intestinal cells [6].
There are many unknown variables The C. elegans and N. parisii relationship allow researchers an opportunity to study the specific mechanisms of microsporidia pathogenicity and other intracellular microbes that thrive in the intestines of other organisms [6]. There are many reasons as to why N. parisii is such a unique pathogen. For one matter, C. elegans is still able to survive and reproduce successfully with high cellular infestation by N. parisii, which means that there is a significant coevolution between the two [4,6,7]. In fact, even if all of its intestinal cells are filled with N. parisii spore cells, C. elegans still moves and appears normal initially, despite the lethality of the infestation [6]. Gradually over time, as the volume of the microsporidian spores increase, C. elegans begins to have sluggish movements [5]. Although N. parisii causes a lethal infestation of only intestinal tissues, but the effects of N. parisii on C. elegans are unclear as the pathogen is isolated only to intestinal cells and has evolved to cause minimal impact on its host [3,6].

Nematocida parisii Cell Shape, Components, and Metabolism


Infection and Spread of N. parisii in C. elegans


Characterization of Nematocida parisii infection stages in C. elegans.
A) Visual of N. parisii infection of C. elegans intestinal cells (green) from sporoplasm invasion to meront formation to replication and formation of spores.
B) DIC images of dissected animals showed various stages of infection. Arrows point out large spores.
C) FISH (red) and DAPI (blue) staining of N. parisii at various stages of infection.

Image source: http://genome.cshlp.org/content/22/12/2478.full.pdf+html [3]

N. parisii is transmitted horizontally from animal to animal [6]. N. parisii enters the intestinal region of C. elegans through either oral consumption or rectal entrance. It infects C. elegans intestinal cells during its transmissible spore form, outlined in Figure 3A [7]. Following the identical spore germination outlined in microsporidia, N. parisii spores invert their polar filament to form a polar tube. The polar tube breaks through the cell wall and cell membrane of the spore and launches itself through the cell membrane of a nearby host cell, in this case the C. elegans intestinal cell. The polar tube serves as a bridge between the spore and the intestinal cell and injects the N. parisii sporoplasm into the C. elegans intestinal cell. Sporoplasm becomes a meront and develops to generate mature spores. Figure 3B gives phase-by-phase visual of post-sporoplasm injection in C. elegans and the development of meront to how the host cell becomes filled with Ni parisii spores. Figure 3C gives a visual of the rapid spore replication during the time of replication. Notice as the N. parisii (red) take over the C. elegans intestinal cells (blue), but they do not disappear. Usually when pathogens such as viruses produce progeny in a host cell, the cell lyses and release all the progeny viruses out. However, from the stain, there is a reasonable concentration of purple in the area where intestinal cells were located, indicating the cells are still alive [5]. As it turns out, mature N. parisii spores are able to exit the host cell without causing severe damage to the cell. N. parisii is able to manipulate the host cell’s cytoskeleton to commit non-lytic escape [7].


Electron microscope analysis of N. parisii infection in intestinal cells show that the presence of N. parisii in the intestinal cell results in alteration of the terminal web [6,7]. The terminal web is a cytoskeletal structure found in many polarized epithelial cells [6]. N. parisii is able to rearrange ACT-5, a specialized actin isoform that is associated with both the terminal web and microvilli of C. elegans. ACT-5 is relocalized from the apical side to the ecotopical basolacteral side of the cell [7]. The actin relocalization that occurred leave gaps in the terminal web, approximately 1 µm-wide [7]. These gaps allow the N. parisii spores formed from the meront to escape the host cell and into the C. elegans lumen without causing cell lysation. Leaving the host cell alive is beneficial to N. parisii because it keeps the host alive to pass off the pathogen to another healthy host [7].

Current Research on N. parisii


Include some current research in each topic, with at least one figure showing data.




Comparison of infection in wild-type and pmk-1 mutant an in different.
A)
B)
C)
D)
E)
F)

Image Source: http://www.plosbiology.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pbio.0060309&representation=PDF[4]

Conclusion


Overall paper length should be 3,000 words, with at least 3 figures.

References

[1] Keeling, P.J. and Fast, N.M. "Microsporidia: Biology and Evolution of Highly Reduced Intracellular Parasites". "Annual Review Microbiology". 2002. Volume 56. p. 93-116.


[2] Xu, Y. and Weiss, L.M. "The Microsporidian Polar Tube: A Highly Specialized Invasion Organelle". "Int. K. Parasitol." 2011. Volume 35 Issue 9. p. 941-953.


[3] Hodgkin, J. and Partridge, F.A. "Caenorhabditis elegans Meets Microsporidia: The Nematode Killers from Paris". "PLoS Biology". 2008. Volume 6 Issue 12. p. 2634-2637.


[4] Cuomo, C.A., Desjardins, C.A., Bakowski, M.A., Goldberg, J., Ma, A.T., Becnel, J.J., Didier, E.S., Fan, L., Heiman, D.I., Levin, J.Z., Young, S., Zheng, Q., and Troemel, E.R. "Microsporidian Genome Analysis Reveals Evolutionary Strategies for Obligate Intracellular Growth". "Genome Research". 2012. Volume 22. p. 2478-2488.


[5] Tromel, E.R., Felix, M., Whiteman, N.K., Barriere, A., and Ausubel, F.M. "Microsporidia are Natural Intracellular Parasites of the Nematoda Caenorhabditis elegans"."PLoS". 2008. Volume 6 Issue 12. p. 2736-2752.


[6] Ardila-Garcia, A.M. and Fast, N.M. "Microsporidian Infection in a Free-Living Marine Nematode". "ASM Eurkaryotic Cell". 2012. Volume 11 Issue 12. p. 1544-1551.


[7] Estes, K.A., Szumowski, S.C., and Troemel, E.R. "Non-Lytic, Actin-Based Exit of Intracellular Parasites from C. elegans Intestinal Cells". "PLoS Pathogens". 2011. Volume 7 Issue 9. p. 1-16.


[8] Moretto, M.M., Khan, I.A., and Weiss, L.M. "Gastrointestinal Cell Mediated Immunity and the Microsporidia". "PLoS Pathogens". 2012. Volume 8 Issue 7. p. 1-4.


[9] Slonczewski, J.L. and Foster, J.W. Microbiology: An Evolving Science. "W.W. Norton & Company, Inc." 2013. Third Ed.

Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2014, Kenyon College.