31-547: The Rhodocyclales are an order of the class Betaproteobacteria in the phylum Pseudomonadota ("Proteobacteria"). Following a major reclassification of the class in 2017, the previously monofamilial order was split into three families: The genus Azovibrio also falls within the order but is incertae sedis , falling between the Zoogloeaeceae and the Azonexaceae . This Betaproteobacteria -related article
62-866: A broad variety of metabolic strategies and occupy diverse environments, ranging from obligate pathogens living within host organisms to oligotrophic groundwater ecosystems. Whilst most members of the Betaproteobacteria are heterotrophic , deriving both their carbon and electrons from organocarbon sources, some are photoheterotrophic , deriving energy from light and carbon from organocarbon sources. Other genera are autotrophic , deriving their carbon from bicarbonate or carbon dioxide and their electrons from reduced inorganic ions such as nitrite , ammonium , thiosulfate or sulfide — many of these chemolithoautotrophic . Betaproteobacteria are economically important, with roles in maintaining soil pH and in elementary cycling. Some economically important members of
93-466: A classic model organism in the field of cell biology. From just 30 L of simple medium inoculated with A. castellanii , about 1 kg of cells can be obtained after several days of aerated culture at room temperature. Pioneered in the laboratory of Edward D. Korn at the National Institutes of Health (NIH), many important biological molecules have been discovered and their pathways elucidated using
124-432: A failure to wash hands prior to handling the lenses. Multipurpose contact lens solutions are largely ineffective against Acanthamoeba , whereas hydrogen peroxide-based solutions have good disinfection characteristics. The first cure of a corneal infection was achieved in 1985 at Moorfields Eye Hospital . In May 2007, Advanced Medical Optics, manufacturer of Complete Moisture Plus Contact Lens Solution products, issued
155-613: A neurotransmitter acetylcholine in Acanthamoeba and the enzymatic machinery needed for its synthesis. Acanthamoeba spp. contain diverse bacterial endosymbionts that are similar to human pathogens, so they are considered to be potential emerging human pathogens. The exact nature of these symbionts and the benefit they represent for the amoebic host still have to be clarified. These include Legionella and Legionella -like pathogens. The giant viruses Mimivirus , Megavirus , and Pandoravirus infect Acanthamoeba . Members of
186-538: A voluntary recall of their Complete Moisture Plus solutions. The fear was that contact lens wearers who used their solution were at higher risk of acanthamoebic keratitis than contact lens wearers who used other solutions. The manufacturer recalled the product after the Centers for Disease Control in the United States found that 21 people had possibly received an Acanthamoeba infection after using Complete Moisture Plus in
217-469: Is a stub . You can help Misplaced Pages by expanding it . Betaproteobacteria Burkholderiales Ferritrophicales Ferrovales Neisseriales Nitrosomonadales Procabacteriales Rhodocyclales Betaproteobacteria are a class of Gram-negative bacteria , and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria). The Betaproteobacteria comprise over 75 genera and 400 species. Together, they represent
248-512: Is a list of described species of Acanthamoeba , with sequence types noted where known. Species that have been identified in diseased patients are marked with *. From the Greek akantha (spike/thorn), which was added before "amoeba" (change) to describe this organism as having a spine-like structure ( acanthopodia ). This organism is now well known as Acanthamoeba , an amphizoic, opportunistic, and nonopportunistic protozoan protist widely distributed in
279-519: Is capable of some form of meiosis and may be able to undergo sexual reproduction. Furthermore, since Acanthamoeba diverged early from the eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Owing to its ease and economy of cultivation, the Neff strain of A. castellanii , discovered in a pond in Golden Gate Park in the 1960s, has been effectively used as
310-413: Is characterized by neurological symptoms including headache, seizures, and mental-status abnormalities. These worsen progressively over weeks to months, leading to death in most patients. Infection is generally associated with underlying conditions such as immunodeficiency , diabetes, malignancies, malnutrition, systemic lupus erythematosus , and alcoholism. The parasite enters the body through cuts in
341-434: Is often but not always seen in immunosuppressed patients. GAE is caused by the amoebae entering the body through an open wound and then spreading to the brain. The combination of host immune responses and secreted amoebal proteases causes massive brain swelling resulting in death in about 95% of those infected. Granulomatous amoebic encephalitis (GAE) is caused by amoebic infection of the central nervous system (CNS). It
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#1732858707148372-624: Is potentially dangerous because high ammonium content can lead to eutrophication . Biological wastewater treatment systems, as well as other biological ammonium-removing methods, depend on the metabolism of various Bacteria including members of the Nitrosomonadales of the Betaproteobacteria that perform nitrification to remove excessive ammonia from wastewater. The ammonia is first oxidized into nitrite , further oxidized to nitrate . A variety of other organisms then reduces nitrate into molecular nitrogen gas ( denitrification ), which leaves
403-629: The Burkholderiales , the Neisseriales , the Nitrosomonadales and the Rhodocyclales . The name " Procabacteriales " was also proposed for an order of endosymbionts of Acanthamoeba , but since they cannot be grown in culture and studies have been limited, the name has never been validly or effectively published, and thus is no more than a nickname without any standing in nomenclature. An extensive reclassification of families and orders of
434-951: The Nitrosomonadales . The four orders of the Betaproteobacteria are: Some members of the Betaproteobacteria can cause disease in various eukaryotic organisms, including humans. For example, Neisseria gonorrhoeae and N. meningitidis cause gonorrhea and meningitis respectively, while Bordetella pertussis causes whooping cough . Other members of the class infect plants, such as Ralstonia solanacearum which causes bacterial wilt disease of over 250 plant species, Burkholderia cepacia which causes bulb rot in onions, and Xylophilus ampelinus which causes necrosis of grapevines. Betaproteobacteria play an important role in denitrification, removal of phosphorus, and xenobiotic degradation from waste. Various human activities, such as fertilizer production and chemical plant usage, release significant amounts of ammonium ions into rivers and oceans. Ammonium buildup in aquatic environments
465-502: The Acanthamoeba model. Thomas Dean Pollard applied this model at the NIH, Harvard Medical School , Johns Hopkins University School of Medicine , and the Salk Institute for Biological Studies to discover and characterize many proteins that are essential for cell motility, not only in amoebae, but also in many other eukaryotic cells, especially those of the human nervous and immune systems,
496-427: The Betaproteobacteria use nitrate as their terminal electron acceptor and can be used industrially to remove nitrate from wastewater by denitrification . A number of Betaproteobacteria are diazotrophs , meaning that they can fix molecular nitrogen from the air as their nitrogen source for growth – this is important to the farming industry as it is a primary means of ammonium levels in soils rising without
527-431: The breakdown of organic matter in soil, contributing to the microbial loop . Because Acanthamoeba does not differ greatly at the ultrastructural level from a mammalian cell, it is an attractive model for cell-biology studies; it is important in cellular microbiology, environmental biology, physiology, cellular interactions, molecular biology, biochemistry, and evolutionary studies, due to the organisms' versatile roles in
558-608: The case that the Acanthamoeba is diagnosed correctly, the current treatments, such as amphotericin B , rifampicin , trimethoprim - sulfamethoxazole , ketoconazole , fluconazole , sulfadiazine , or albendazole , are only tentatively successful. Correct and timely diagnosis, as well as improved treatment methods and an understanding of the parasite, are important factors in improving the outcome of infection by Acanthamoeba . A paper published in 2013 has shown substantial effects of some FDA-approved drugs with an in vitro kill rate above 90%. These results were in vitro effects, but as
589-470: The class based on a polyphasic analysis (including 16S rRNA gene analyses and 53-protein ribosomal protein concatamer analyses using the rMLST Multilocus sequence typing system) was published in 2017, that removed the order Hydrogenophilales from the class and into a novel class of the " Pseudomonadota ", the Hydrogenophilalia . The same study also merged the former order Methylophilales into
620-994: The developing embryo, and cancer cells. Acanthamoeba also has served as a model to study the evolution of certain G-proteins. This unicellular eukaryote expresses few GPCRs over its cell membrane that serve vital role for the microorganism, structural homology bioinformatics tools have been used to show the presence of a homolog of human M1-muscarinic receptor in A. castellanii . Blocking these muscarinic receptors in past studies has proven to be amoebicidal in Acanthamoeba spp. More recently, voltage-gated calcium channels in Acanthamoeba spp. (CavAc) have been reported to have similarities with human voltage-gated calcium channels such as TPC-1 and L-type calcium channels and respond to Ca-channel blockers such as loperamide. This model microbe has been studied to understand complex neurodegenerative states including Alzheimer's disease. Scientists have isolated
651-409: The drugs are already approved, human infections can be targeted after dose calculations in clinical trials done with these diverse groups of drugs. When present in the eye, Acanthamoeba strains can cause acanthamoebic keratitis , which may lead to corneal ulcers or even blindness. This condition occurs most often among contact lens wearers who do not properly disinfect their lenses, exacerbated by
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#1732858707148682-634: The ecosystem and ability to capture prey by phagocytosis , act as vectors and reservoirs for microbial pathogens, and to produce serious human infections. In addition, Acanthamoeba has been used extensively to understand the molecular biology of cell motility and cancer cell dormancy by in-depth exploration of the process of encystation. The recently available Acanthamoeba genome sequence revealed several orthologs of genes employed in meiosis of sexual eukaryotes . These genes included Spo11 , Mre11 , Rad50 , Rad51 , Rad52 , Mnd1, Dmc1 , Msh , and Mlh . This finding suggests that Acanthamoeba
713-579: The ecosystem and is carried into the atmosphere. Acanthamoeba Acanthamoeba is a genus of amoebae that are commonly recovered from soil, fresh water , and other habitats . The genus Acanthamoeba has two stages in its life cycle, the metabolically active trophozoite stage and a dormant, stress-resistant cyst stage. In nature, Acanthamoeba species are generally free-living bacterivores . However, they are also opportunistic pathogens able to cause serious and sometimes fatal infections in humans and other animals. Acanthamoeba spp. are among
744-606: The genus Acanthamoeba are unusual in serving as hosts for a variety of giant viruses (that have more than 1000 protein-coding genes; for instance, Pandoravirus , which has about 2500 protein-coding genes in its genome). Acanthamoeba can be distinguished from other genera of amoebae based on morphological characteristics. However, differentiating one species of Acanthamoeba from another by morphology has proven difficult. Based on 18S rDNA sequencing, known Acanthamoeba strains can be organized into 12 groups, denoted T1-T12. Most disease-causing isolates belong to type T4. Below
775-431: The high prevalence of Acanthamoeba in the environment, these amoebae have been proposed to serve as an environmental reservoir for some human pathogens. A. castellanii can be found at high densities in various soil ecosystems. It preys on bacteria, but also fungi and other protozoa. This species is able to lyse bacteria and produce a wide range of enzymes, such as cellulases or chitinases, and probably contributes to
806-489: The month prior to diagnosis. Several species of bacteria that can cause human disease are also able to infect and replicate within Acanthamoeba species. These include Legionella pneumophila , Pseudomonas aeruginosa , and some strains of Escherichia coli and Staphylococcus aureus . For some of these bacteria, replication inside Acanthamoeba has been associated with enhanced growth in macrophages, and increased resistance to some antibiotics. Furthermore, due to
837-540: The most prevalent protozoa found in the environment. They are distributed worldwide, and have been isolated from soil, air, sewage, seawater, chlorinated swimming pools, domestic tap water, bottled water, dental treatment units, hospitals, air-conditioning units, and contact lens cases. Additionally, they have been isolated from human skin, nasal cavities, throats, and intestines, as well as plants and other mammals. Diseases caused by Acanthamoeba include keratitis and granulomatous amoebic encephalitis (GAE). The latter
868-754: The patients do not have adequate numbers of CD+ve T-cells to mount a granulomatous response to Acanthamoeba infection in CNS and other organs and tissues. A perivascular cuffing with amoebae in necrotic tissue is usual finding in the AIDS and related T-cell immunodeficiency conditions. Brain biopsy normally reveals severe oedema and hemorrhagic necrosis . A patient who has contracted this illness usually displays subacute symptoms, including altered mental status, headaches, fever, neck stiffness, seizures, and focal neurological signs (such as cranial nerve palsies and coma), all leading to death within one week to several months. Due to
899-549: The presence of leguminous plants . The Betaproteobacteria are one of the eight classes that make up the Pseudomonadota ("Proteobacteria"). The Betaproteobacteria are most closely related to the Gammaproteobacteria , Acidithiobacillia and Hydrogenophilalia , which together make up a taxon which has previously been called " Chromatibacteria ". Four orders of Betaproteobacteria are currently recognised —
930-564: The rarity of this parasite and a lack of knowledge, no good diagnoses or treatments for Acanthamoeba infection are now known. Acanthamoeba keratitis cases in the past have resolved from a therapy consisting of atropine and some other drugs with no antimicrobial effects. Recent publications show atropine to interfere with the protist's CHRM1 receptor, causing cell death. Infection usually mimics that of bacterial leptomeningitis , tuberculous meningitis , or viral encephalitis. The misdiagnosis often leads to erroneous, ineffective treatment. In
961-457: The skin or by being inhaled into the upper respiratory tract. The parasite then spreads through the blood into the CNS. Acanthamoeba crosses the blood–brain barrier by means that are not yet understood. Subsequent invasion of the connective tissue and induction of pro-inflammatory responses leads to neuronal damage that can be fatal within days. Pure granulomatous lesions are rare in patients with AIDS and other related immunodeficiency states, as