Naegleria fowleri

A Microbial Biorealm page on the genus Naegleria fowleri

Classification

Higher order taxa

Eukaryota, Percoloza, Heterolobosea, Schizopyrenida, Vahlkampfiidae, Naegleria, fowleri

Species

NCBI: Taxonomy

Naegleria fowleri

Description and significance

Naegleria fowleri are found in warm bodies of water across the globe. It is responsible for causing over 300 cases of primary amoebic meningoencephalitis, or PAM, of which there are only seven survivors. Its ability to transform into a bi-flagellate stage has increased interest in this microorganism and it's use as a model for differentiation in eukaryotic cells (G).

Genome structure

Few studies have been done involving the genome of Naegleria fowleri, though some important information has been discovered. Although it is known that N. fowleri is polyploidy,the exact number of genome copies is unknown (E). Its genome size was orginally estimated at over 70.6 kbp, obtained by summing the 16.5kpb ribosomal DNA and its 54.1kpb mitochondrial DNA (A). Both the rDNA and mtDNA sizes were calculated by restriction endonuclease fragments. Further research has discovered a 104 kbp genome with 23 chromosomes (G). The rDNA is kept on extrachomosonal, circular plasmids called episomes ranging in size from 14kpb to 17kbp. As the entire genome is polyploidy, these eposomes are multicopy episomes up to 4000 copies. Species classification is done using either 5.8s rDNA or SSUrDNA (G)

Life Cycle

Naegleria fowleri exist in three stages; cyst, amoebiod trophozoites and flagellated trophozoite. At less than ideal conditions (below 27^oC), the amoeba forms a spherical cyst, approximately 7-14μm. In the cyst stage, the single nucleus is protected by a dense cell wall and a a very granular cytosol. The cell wall generally contains two pores which are plugged with mucus until trophozoite stage is induced (C). When the cyst is activated, binary fission occurs into the trophozoite stage. The trophozoite stage is not only the only stage in which N. fowleri can grow, it is also the active and infectious stage of the life cycle (B). In this primary trophozoite stage, the cells are between 10-30 mu;m characterized by a dark, central nucleus (C). Many vacuoles are seen in the cytoplasm which aid in the cell's movement by lobopodia (D). An intermediate flagellate trophozoite stage is also observed in some, but not all strains of N. fowleri. These pear shaped, lophotichous cells use 2 flagella on one end of the cell for movement in finding a suitable host. This transformation into the flagellated stage can be induced by changing the environment of the bacteria, even as simply as being placed in distilled water (C).

Cell structure and metabolism

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Ecology

Naegleria fowleri are found world wide in warm freshwater, either naturally geothermic pools or warm bodies of water created by industry such as industrial cooling water (H). Although they ideally grow at 37^oC, the temperature of their human hosts, below 27^oC, N. fowleri are able to survive by encysting. The amoeba is able to grow in environments up to 45^oC (D). Although it is found all across the globe, the only place where N. fowleri contaminates public drinking water is in South Australia (H). It has even been found in poorly chlorinated pools in southern regions of the United States and other warm locales. This widespread finding of N. fowleri and the low number of cases of N. fowleri related PAM lead to the belief that many more humans are exposed to N. fowleri than actually become infected.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Current Research

Enter summarries of the most rescent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.