Acanthamoeba polyphaga
Introduction
Acanthamoeba polyphaga is a free-living amoeba found in environments including soil, dust, air, seawater, tap water, and swimming pools [1].
A. polyphaga receives nutrition by consuming bacteria, algae, and yeast via phagocytosis. The amoeba ingests liquids through the process of pinocytosis. A. polyphaga acts as a secondary decomposer to remineralize soil with carbon, nitrogen, and phosphorous by consuming bacterial primary decomposers. Primary decomposers decompose organic material into minerals, but can not release these minerals from their own mass. After A. polyphaga digests the primary decomposers, the amoeba uses contractile vacuoles to release the environmentally useful bacterial nutrients from its food vacuole into the soil [1].
A. polyphaga, like the rest of the Acanthamoeba species, is divided into two lifecyles: the active trophozoite stage which reproduces via binary fission and the dormant, non-dividing cyst stage. Acanthamoeba polyphaga trophozoites contain one or more contractile vacuoles, lysosomes, digestive vacuoles, glycogen-containing vacuoles, a Golgi complex, smooth and rough endoplasmic reticulum, free ribosomes, microtubules, large numbers of mitochondria, and a single nucleus [1, 2]. The cysts of A. polyphaga contain durable double walls for protection in harsh conditions. The trophozoite turns into a cyst under adverse environmental conditions such as during food deprivation, desiccation, and changes in temperature and pH [1].
Other examples:
Bold
Italic
Subscript: H2O
Superscript: Fe3+
Classification
Acanthamoeba are termed amphizoic organisms due to their ability to exist as either free-living or parasitic. Identification at the genus level is easy to detect since all Acanthamoeba trophozoites contain spiny projections on the surfaces of their cell [1].
The species level has three morphological groups (I, II, and III) based on cyst size and shape. Species I have larger cysts, species II have a wrinkled outer cyst and a stellate inner cyst, and species III have a smooth ectocyst and a round endocyst. A. polyphaga is placed in the Species II group since it is characterized as having a wrinkled ectocyst and a stellate endocyst [1].
The accurate placement of species into one of the three group levels is difficult since cyst structure changes depending on environmental factors. Categorizing the species into immunological categories based on outward cell conditions is difficult since some species share antigenic or antibody determinants. The enzymatic patterns within the Acanthamoeba have been used to group individuals, but similarities exist between strains of separate species [1].
Due to the current inconsistencies of morphological, DNA-based approaches and biochemical criteria commonly used for classification, researchers are attempting to revise the Acanthamoeba species taxonomy based on nucleotide sequences of subunit rRNAs [1].
Granulomatous Amebic Encephalitis (GAE)
A. polyphaga can be pathogenic to humans with compromised immune systems and cause a rare but fatal nervous system disease called Granulomatous Amebic Encephalitis (GAE) [1]. The amoeba enters the body through the respiratory tract and invades the alveolar blood vessels, ultimately passing through the blood-brain barrier and entering the central nervous system (CNS) [2].
Diagnosis is difficult because symptoms of GAE are vague and resemble other common diseases. The symptoms include headache, fever, lethargy, stiff neck, and vomiting. A. polyphaga is not always detected in human serum and therefore cannot be detected when cultured. In severely immunocompromised patients, the brain lesions may not appear on magnetic resonance imaging (MRI) or on computerized tomography (CT scan). Thus, patients usually die before the protozoan is detected and identified. There is a greater than 90% mortality rate [2]. Currently, many patients are diagnosed during the autopsy by examination of brain tissue after death has already occurred [3].
Recently, researchers have detected A. polyphaga DNA obtained from samples of cerebral spinal fluid by lumbar puncture. The samples of centrifuged cerebral spinal fluid in conjunction with Polymerase Chain Reaction (PCR) gel technique have revealed the presence of Acanthamoeba. This discovery may lead to earlier detection and treatment options for immunocompromised patients suffering from Acanthamoeba infections [3].
Section 3
Include some current research in each topic, with at least one figure showing data.
Conclusion
Overall paper length should be 3,000 words, with at least 3 figures.
References
Edited by (your name here), a student of Nora Sullivan in BIOL187S (Microbial Life) in The Keck Science Department of the Claremont Colleges Spring 2013.