Mycoplasma gallisepticum
A Microbial Biorealm page on the genus Mycoplasma gallisepticum
Classification
Higher order taxa
Bacteria; Firmicutes; Mollicutes; Mycoplasmatales; Mycoplasmataceae; Mycoplasma; gallisepticum
Species
Candidatus Mycoplasma haematoparvum, Candidatus M. haemobos, Candidatus M. haemodidelphidis, Candidates M. haemolamae, Candidatus M. haemominutum, Candidatus M. kahanei, Candidatus M. ravipulmonis, Candidatus M. turicensis, M. adleri, M. agalactiae, M. agassizii, M. alkalescens, M. alligatoris, M. alvi, M. amphoriforme, M. anatis, M. anseris, M. arginini, M. arthritidis, M. auris, M. bovigenitalium, M. bovirhinis, M. bovis, M. bovoculi, M. buccale, M. buteonis, M. californicum, M. canadense, M. canis, M. capricolum, M. caviae, M. cavipharyngis, M. citelli, M. cloacale, M. coccoides, M. collis, M. columbinasale, M. columbinum, M. columborale, M. conjunctivae, M. corogypsi, M. cottewii, M. cricetuli, M. crocodyli, M. cynos, M. dispar, M. edwardii, M. elephantis, M. equigenitalium, M. equirhinis, M. falconis, M. fastidiosum, M. faucium, M. felifaucium, M. feliminutum, M. felis, M. fermentaus, M. incognitos, M. flocculare, M. gallinaceum, M. gallinarum, M. gallisepticum, M. gallopavonis, M. gateae, M. genitalium M. glycophilum, M. gypis, M. haemocanis, M. haemofelis, M. haemomuris, M. hominis, M. hyopharyngis, M. hyponeumoniae, M. hyorhinis, M. hyosynoviae, M. iguanae, M. imitans, M. indiense, M. iners, M. iowae, M. lagogenitalium, M. leonicaptivi, M. leopharyngis, M. lipofaciens, M. lipophilum, M. maculosum, M. meleagridis, M. microti, M. moatsii, M. mobile, M. molare, M. monodon, M. muris, M. mustelae, M. mycoides, M. neurolyticum, M. opalescens, M. orale, M. ovipneumoniae, M. ovis, M. oxoniensis, M. penetrans, M. phocicerebrale, M. phocidae, M. phocirhinis, M. pirum, M. pneumoniae, M. pneumophila, M. primatum, M. pullorum, M. pulmonis, M. putrefaciens, M. salivarium, M. simbae, M. spermatophilum, M. sphenisci, M. spumans, M. sturni, M. sualvi, M. subdolum, M. suis, M. synoviae, M. testudineum, M. testudinis, M. timone, M. verecundum, M. vulturii, M. wenyonii, M. yeatsii, M. zalophi
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NCBI: Taxonomy |
Description and significance
M. gallisepticum is a bacterial pathogen that results in chronic respiratory disease. It is found in the respiratory system of poultry and other avian species at a temperature of 37°C. The pathogen lacks a cell wall, has a flask-shaped appearance, blebs at the poles of the cell and specialized tip-like organelles. Depending on the environment, M. gallisepticum can survive from a few days to months. On cotton, rubber, hair and feathers, M. gallisepticum can survive between one and four days. In dry conditions at 4°C it can survive 61 days and at 20°C, survive 10 to 14 days. The sequencing of the genome was to determine the pathogenic mechanism of virulence of the bacterium. A clone of the strain Rlow designated Rlowc2 (isolated from the respiratory system of chickens and the respiratory organs, eyes and brains of avian species) was used to sequence the genome of M. gallisepticum.
Genome structure
The circular DNA genome of M. gallisepticum is 996,422 bp long with a G+C content of 31mol%. 742 coding DNA sequences (CDSs), 91% coding density, have been determined of the 996,422 bp. Of the 742 CDSs, functions of 469 coding DNA sequences have been determined, 159 CDSs are conserved hypothetical proteins and the remaining 123 CDSs are hypothetical proteins. 33 tRNA genes were identified in the genome along with a polypeptide release factor prfA (similar to DNA transcription UAA and UAG stop codons). M. gallisepticum's genome contains two 16s rRNA genes.
Like M. pneumoniae and M. genitalium, M. gallisepticum’s genes within the OriC region are not conserved. Genes in the OriC region include: gyrA, gyrB, dnaJ, dnaN, soj (upstream of dnaA), and ABC transporters, rpl34 and rpnA (downstream of dnaA). The origin of replication contains an increased number of A•T base pairs (characteristic of prokaryotes) found between the dnaN and soj genes.
The genome of M. gallisepticum contains genes, including VlhA, also known as pMGA lipoproteins, that make up the largest family of genes. This family is noted as the vlhA family that generates an antigenic variation in chickens and avian species, and is important in allowing the bacteria to evade the hosts’ immune response. The vlhA family consists of 43 genes making up a total 43kb of the bacterial genome.
Cell structure and metabolism
M. gallisepticum is a cell wall lacking bacterium. It contains filaments that allow the bacterium to adhere to the host(erythrocyte) for colonization. By electron microscopy a “unit” membrane, granular nuclear material, cylindrical ribosomal arrays and surface blebs can be seen within the bacterium.
M. gallisepticum’s cell membrane is a 110A “unit” membrane containing intramembranous particles approximately 5 to 10nm in diameter. The membrane consists of two 30A lines separated by a 50A area. The membrane contains many different membrane-associated proteins: ATP binding proteins, SecA, FtsY, and proteases. 24 ATP–binding proteins in the membrane are found associated with the ABC transporter making up the second largest gene family in M. gallisepticum. This family constitutes one-third of the total 75 proteins predicted to be involved in biomolecule transport. The membrane proteins SecA, SecE, SecY, YidC and a trigger factor are involved in membrane-associated protein secretion, and FtsY and Ffh are involved in signal recognition particle pathway. Several transmembrane domains found from the VlhA family include GDSL motif, zinc metalloproteases, and lectin-binding motifs, suggesting that some membrane-associated proteins can bind portions of sugar for the purpose of cytadherence and nutrient uptake.
The bacterium’s nuclear material containing the DNA is found in a centrally located region as a fibril containing granules smaller than ribosomes. The fibril is 30A in thickness. Bleb shaped structures make up the anterior of the cell, measuring 800A by 1,300A, excluding the bounding membrane.
M. gallisepticum produces dihydrolipoamide transacetylase and pyruvate dehydrogenate enzymes, part of the multienzyme pyruvate dehydrogenase complex (PDHC). With these enzymes, pyruvate oxidation occurs, producing acetyl-CoA and generating ATP, the bacteria’s source of energy. Also included is the ATP binding cassette transporters, an important transport system needed to acquire many precursors needed for the bacteria’s survival.
Ecology and Pathology
M. gallisepticum causes chronic respiratory disease in poultry, most commonly found in chicken, and other avian species. The bacteria is transmitted through direct contact of infected species or transmission through the environment, dust, soil, drinking water, food, etc., causing an environmental loss in poultry and egg production.
Chronic respiratory disease is caused via cytadherence to sialic acid residues of the tracheal lumen epithelial cells to the tip-like structures of M.gallisepticum’s virulent R strain. Two genes, CrmA and GapA are essential to the cytadherence of M. gallisepticum. Attachment to the epithelial cells is the prerequisite for cytopathogenicity, which eventually leads to the fusion of the cell membrane with M. gallisepticum. Penetration of M. gallisepticum into cells can occur within 5 minutes after infection, increasing the number of intracellular mycoplasmas in 24 hours. Secondary infection through ciliostasis and deciliation of the tracheal epithelium allows other bacterial and viral pathogens to infect erythrocytes. The cause of the this pathogen’s virulence is through the family of genes vlhA, a virulent factor includes the protein Lpd, from the family of genes vlhA, that causes this colonization and pathogenesis. Symptoms of this disease are nasal discharge, decreased egg production, tracheal rales, and weight loss.
Current Research
1. Research at the University of Melbourne current performed by Dr. Philip Markham is underway to investigate the behavior of the approximately 700 genes of the bacteria M. gallisepticum. The research is to identify the weaknesses of the M. gallisepticum which the allow chicken’s immune system can “capitalise on.”
2. Cheryl Jenkins, Steven J. Geary, Martha Gladd, and Steven P. Djordjevic. “The Mycoplasma gallisepticum OsmC-like protein MG1142 resides on the cell surface and binds heparin” Microbiology. 2007. Volume 153. p. 1455-1463 Research performed of M. gallisepticum’s MG1142 protein and heparin have found that MG1142 is able to bind to heparin which may be involved in adherence of the bacteria to the host and may lead to pathogenicity. Research is currently underway to investigate the interaction between the bacterium M. gallisepticum and the host’s extracellular matrix(human lung fibroblast cell line), leading to future studies of the effects of heparin and other extracellular matrix on M.gallisepticum’s ability to bind tissues or cell lines from avian sources.
References
1. S. Razin, M. Banai, H. Gamliel, A. Polliack, W. Bredt, and I. Kahane. “Scanning electron microscopy of mycoplasmas adhereing to erythrocytes”. Infection and Immunity. 1980. Volume 30. p. 538-546
2. Leka Papazisi, Timothy S. Gorton, Gerald Kutish, Philip F. Markham, Glenn F. Browning, Di Kim Nguyen, Steven Swartzell, Anup Madan, Greg Mahairas, and Steven J. Geary “The complete genome sequence of the avian pathogen Mycoplasma gallisepticum strain Rlow”.Microbiology. 2003. Volume 149 p. 2307-2316
3. Osama M. Saed Abdul-Wahab, Gordon Ross, and Janet M. Bradbury. “Pathogenicity and Cytadherence of Mycoplasma imitans in Chicken and Duck Embryo Trachael Organ Cultures”. Infection and Immunity. 1996. Volume 68. p. 563-568
4. Florian Winner, Renate Rosengarten, and Christine Citti. “In Vitro Cell Invasion of Mycoplasma gallisepticum”. Infection and Immunity. 2000. Volume 68. p. 4238-4244
5. Jack Maniloff, Harold J. Morowitz, and Russell J. Barrnett. “Ultrastructure and Ribosomes of Mycoplasma gallisepticum”. Journal of Bacteriology. 1965. Volume 90. p. 193-204
6. Corinne Marois, Fabienne Dufour-Gesbert, and Isabelle Kempf, “Polymerase chain reaction for detection of Mycoplasma gallisepticum in environmental samples”, Avian Pathology, 31:2, 163 – 168
7. M. Banai, I. kahane, S. Razin, and W. Bredt. “Adherence of Mycoplasma gallisepticum to Human Erythrocytes”. Infection and Immunity. 1978. Volume 21, p.365-372
8. P. Hudson, T. S. Gorton, L. Papazisi, K. Cecchini, S. Frasca, Jr. and S. J. Geary. “Identification of a Virulence-Associated Determinant, Dihydrolipoamide Dehydrogenage (lpd), in Mycoplasma gallisepticum through In Vivo Screening of Transposon Mutants”. Infection and Immunity. 2006. Volume 74, p. 931-939
9. Cheryl Jenkins, Steven J. Geary, Martha Gladd, and Steven P. Djordjevic. “The Mycoplasma gallisepticum OsmC-like protein MG1142 resides on the cell surface and binds heparin” Microbiology. 2007. Volume 153. p. 1455-1463
10. S. Boguslavsky, D. Menaker, I. Lysnyansky, T. Liu, S. Levisohn, R. Rosengarten, M. Garcia, and D. Yogev. “Molecular Characterization of the Mycoplasma gallisepticum pvpA Gene Which Encodes a Putative Variable Cytadhesin Protein”. Infection and Immunity. 2000. Volume 68. p. 3956-3964
Edited by Tawny Issarapanichkit, student of Rachel Larsen and Kit Pogliano
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