Naegleria

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A Microbial Biorealm page on the genus Naegleria

Classification

Higher Order Taxa

Eukaryota; Heterolobosea; Schizopyrenida; Vahlkampfiidae

Species

N. americana, N. andersoni, N. angularis, N. antarctica, N. arctica, N. australiensis, N. canariensis, N. carteri, N. chilensis, N. clarki, N. dobsoni, N. dunnebackei, N. endoi, N. fowleri, N. fultoni, N. galeacystis,

N. gallica, N. gruberi, N. indonesiensis, N. italic, N. jadini, N. jamiesoni, N. laresi, N. lovaniensis, N. mexicana, N. minor, N. morganensis, N. neoantarctica, N. neochilensis, N. neodobsoni, N. neopolaris,

N. niuginesis, N. pagei, N. paradobsoni, N. peruana, N. philippinensis, N. polaris, N. pringsheimi, N. pussardi, N. robinsoni, N. schusteri, N. spitzbergeniensis, N. sturti, N. tenerifensis, N. tihangensis

NCBI: Naegleria

Description,Significance, and Ecology

Naegleria is a diverse genus of protozoan that is generally diphasic, beginning in an amoeboid form and then entering a flagellate form. This results in the microbes being referred to as amoebo-flagellates. Naegleria are generally free living and can be found in both water and soil. These microbes feed mainly on bacteria. There are more than one hundred species of Naegleria but only a few are pathogenic (Center for Disease Control and Prevention, 2008).

When Naegleria in soil or on some other solid are exposed to liquid such as water and have their food source removed, they undergo the transformation into di-flagellate form. This form aids them in dispersal to a more desirable location. Oddly enough, they do not persist in this form, returning to the amoeboid form in a matter of hours. The return to amoeboid form is possibly due to the fact that the Naegleria can only feed while in their amoeboid form. Also, reproduction only occurs in the amoeboid form. There is one other, non-active form that Naegleria takes on known as the cyst stage (Caprette, 2007).

Genome Structure

Currently, the only genomic reserach being conducted on the Naegleria genius deals with the species N. gruberi.

The following links contain more imformation on the N. gruberi sequencing project:

Cell Structure and Metabolism

Naegleria is a common genus of amoebo-flagellate protozoa. It is a free living organism. Naegleria are not easy to distinguish morphologically. Their species are defined and identified by the shape of their flagella (Scott, 2008). In contrast to their genus, there are two species of Naegleria that do not develop flagella under laboratory conditions.

Naegleria have a circular ribosomal DNA (Jonckheere, 2002). Naegleria usually have a three stage life cycle. In the first stage, amoeba stage, the morphology of the amoeba is cylindrical, with a size range of 10-30 um, and a contracting area in the rear. This contracting area compresses the cytoplasm allowing locomotion. Naegleria divide by fission.

When Naegleria is diluted naturally by rainwater they rapidly develop into their second stage or flagellate stage. This stage is started from a new transcription from the nucleus (Scott, 2008). Naegleria develop an elongated body and two long anterior flagella. The Naegleria amoeba has to create centrioles that will serve as basal bodies of the flagella. Each flagellum is made up of around 300 proteins that function to allow movement (Scott, 2008). Flagella movement is dependant on the orientation of these proteins in relationship to one another. The flagella do not divide but can revert to the amoeba stage. Then under unfavorable conditions sometimes the initial stage (amoeba stage) can be modify into the third stage that would be a circular cyst (7-14 um) (Bennett, 2008), which is resistant to the hostile environment. In addition to basal bodies, flagella, and a nucleus, Naegleria also have a distinct nuclear envelope, prominent nucleolus, many contractile vacuoles (Chandler & Allan, 1971), cytoplasm, pleomorphic mitochondria and some rough reticulum endoplasmatic.(Patterson et al, 1981)


Pathology

Few Naegleria species have shown to be pathogenic in humans and animals. N. Folweri is a primary example of how bacteria is seen to effect humans and various species of animals, even though there are few cases to be found. This species is an amoeba that is a facultative pathogen capable of living many generations without affecting a host. The host has not been clearly identified because there have been so few cases in humans to term as the primary host. Various other mammals have also been found to be infected such as mice, cotton rats, squirrels, muskrats, guinea pigs, and sheep. Also, fish are found to be frequently parasitized by Naegleria, especially in the gills (University of Edinburgh, 2003).

Both pathogenic and nonpathogenic Naegleria enter through the nose by swimming in warm water and other intimate contacts with warm water. Once inside the body the amoeba makes its way to the brain by means of locomotion where there the destruction of the neurons takes place causing Primary Amoebic Meningoencephalitis (PAM) in humans. This is a disease of the central nervous system that has symptoms similar to that of bacterial meningitis. The only difference is that in PAM there is no cerebrospinal fluid. N. Fowleri possesses secreting proteases, phospholipases, and pore-forming peptides which are all implications of a pathogenic process. Their pathogenicity is found to be in strong correlation with temperature tolerance and therefore most are able to survive within in the human host at the normal 37°C. However most of the PAMcases studies found that N. Fowleri can withstand temperatures up to 45°C. There has been only been about approximately 300 cases worldwide with only seven surviving. Early diagnosis is crucial with the incubation period being only between 3 and 8 days. And the patient usually survives 7 to 10 days after infection (University of Edinburgh, 2003).

Bioremediation

Naegleria can be used in wastewater treatment by participating in anaerobic degradation of organic matter. This is a complex process where microbial organisms, along with biochemical and physic-chemical characteristics work together treating Biodegradable wastewaters.

Researchers have performed experiments in anaerobic continuous stirred tank reactors containing protozoa (some of them from the Naegleria genus), bacteria and archeae organisms. This group of microbes has the ability to degrade natural polymers such as: polysaccharides, proteins, nucleic acids and lipids into methane and carbon dioxide in the absence of oxygen. In this process protozoa reduce MLSS (mix liquid suspended solids), most commonly known as a biomass, and increase sludge activity. Protozoa in anaerobic wastewater treatment increase COD (chemical oxygen demand) removal and increase methane production. Also, Naegleria and other protozoa have the ability to feed on organic matter and not just bacteria. (Priya et al, 2007)

Current Research

The majority of the current scientific research on Naegleria deals with the virulent species N. fowleri, being that it causes amoebic meningoencephalitis (PAM) in animals and humans. Some of the most recent findings are listed below.

From the Department of Microbiology at Ajou University’s School of Medicine, Kim et al. has attempted to examine the effectiveness of miltefosine and chlorpromazine in combating the pathogenic species N. fowleri. Currently, the very toxic amphotericin B is the only antibiotic available for treating PAM; however, it may cause many adverse effects on the patient’s organs. This research has shown that both miltefosine and chlorpromazine are just as effective as amphotericin B in treating PAM caused by N. fowleri, with chlorpromazine exhibiting the most therapeutic potential when considering both effectiveness and lack of negative side effects.

Jamerson et al. surveyed the water of Lake Anna located in Virginia in search for a correlation between the presence of N. fowleri and water conditions. It had been hypothesized that heated water favors N. fowleri’s rapid proliferation, which would in turn increase the risk of human infection at such sites. Their findings exhibited no specific correlation between increased abundance of N. fowleri and the tested water parameters, which included conductivity, dissolved oxygen, temperature, and pH.

Song et al. investigated the N. fowleri heat shock protein 70 (Nf-cHSP70) to determine if it plays a role in the species’ infectious nature. To do this, they compared the affect of a knock-down Nf-cHSP70 gene to a known chemical inhibitor of N. fowleri, benzylidene lactam compound. The chemical produced a 79.4% reduction of N. fowleri proliferation when compared to the control group, while the knock-down of the Nf-cHSP70 gene produced a 68.5% proliferation reduction. An additional similarity in reduction of N. fowleri’s cytotoxicity was also observed when comparing the knock-down with the chemical inhibitor. The research suggests the heat shock protein 70 of N. fowleri may be an important target for potential treatment procedures.

References

  • Jamerson, M., Remmers, K., Cabral, G., & Marciano-Cabral, F. (2008). Survey for the presence of Naegleria fowleri Amebae in lake water used to cool reactors at a nuclear power generating plant. Parasitology Research, in press. Epub ahead of print retrieved December 3, 2008, from <http://www.springerlink.com/content/l0267n47nxg481k5/>
  • John F. De Jonckheere(2002). A Century of Research on the Amoebo-flagellate genus Naegleria.41(44) pp 309-342. Scientific Institute of Public Health, Brussels, Belgium. Retrieved November 23.From <http://www.nencki.gov.pl/pdf/ap/ap632.pdf>
  • Kim, J.H., Jung, S.Y., Lee, Y.J., Song, K.J., Kwon, D., Kim, K., Park, S., Im, K.I., & Shin, H.J. (2008). Effect of therapeutic chemical agents in vitro and on experimental meningoencephalitis due to Naegleria fowleri. Antimicrobial Agents and Chemotherapy, 52, 4010-4016.
  • M.Patterson, T.W.Woodworth, F.Marciano-Cabral and S.G. Bradley(1981).Ultraestructure of Naegleria Fowleri Enflagellation. Journal of Bacteriology.147(1) pp 217-226. Retrieved November 24. From <http://jb.asm.org/cgi/reprint/147/1/217.pdf>
  • Song, K.J., Song, K.H., Kim, J.H., Sohn, H.J., Lee, Y.J., Park, C.E., & Shin, H.J. (2008). Heat shock protein 70 of Naegleria fowleri is important factor for proliferation and in vitro cytotoxicity. Parasitology Research, 103(2), 313-317.

External Links


Edited by student of Dr. Kirk Bartholomew

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