Mycoplasma mobile

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A Microbial Biorealm page on the genus Mycoplasma mobile

Classification

Higher order taxa

Cellular organisms; Bacteria; Firmicutes; Mollicutes; Mycoplasmatales; Mycoplasmataceae; Mycoplasma

Genus and Species

Mycoplasma mobile

NCBI: Taxonomy

Description and significance

Mycoplasma mobile, a flask-shaped piscine mycoplasma (approximately 1.0 x 0.3 µm), is thought to be pathogenic and was first isolated from a tench fish host. Mycoplasma mobile is known for its gliding motility at speeds as fast as 7 µm/second. Many of the mycoplasma organisms have this gliding motility, defined as “a smooth translocation over a solid surface,” but none as extreme as the ability of Mycoplasma mobile. M. mobile has been observed to move in the direction of the tapered end of the cell, known as the “head,” and glides at high speeds without reversing directions or stopping. M. mobile has also been found to be very strong, able to “tow an erythrocyte roughly 10 times its size, without significant loss in speed and has been measured to exert up to 27 pN of force ability.”

Because little has been discovered about the genes responsible for gliding motility, scientists thought it would be useful to sequence the complete genome and proteome of Mycoplasma mobile. They felt that comparing the genomic sequence of M. mobile to those of other immotile or slower-gliding mycoplasmas could help paint a clearer picture of the gliding mechanism. The results of these analyses leave open the possibility that gliding motility might have arisen independently more than once in the mycoplasma lineage.

Genome structure

The M. mobile genome consists of a single circular chromosome. It has been found to have 777,079 bp. Its GC content (24.9 %), is considered low compared other mycoplasmas, which are already typically GC-poor (24%–40%). Scientists investigating Mycoplasma mobile have found coding sequences for 635 proteins in the genome, 88% of which have been shown to be expressed proteins. M. mobile contains a single copy each of the 16S–23S–5S ribosomal DNAs. Unlike as found with other mycoplasma organisms such as the similar M. pulmonis, the 5S rDNA is not located within the 16S–23S rDNA operon, but is located about 180° away (with respect to the circular chromosome) from it. This is an implication that a major genome rearrangement may have occurred about this axis. There was evidence for 28 tRNA genes in the M. mobile genome, the fewest of any organism reported at the time. Other unique features were discovered, including a long repeating unit of DNA of 2435 bp. This DNA unit is present in five copies which code for almost identical proteins, but are uniquely expressed. Many tandem duplications and evidence of lateral gene transfer are present in the M. mobile genome.

Cell structure and metabolism

Mycoplasmas are wall-less bacteria known for having small physical dimensions and genome sizes. Mycoplasma mobile is a flask-shaped mycoplasma, and has been found to be a Gram-positive eubacteria. Scientists interested in the gliding motility of M. mobile have studied the genome but have not found genes similar to other forms of cell motility in bacteria such as flagellae or pili. They also did not find forms of motility similar to those of eukaryotes, such as genes encoding for myosin, kinesin, or actin, which have been found in genome sequences of other gliding mycoplasmas. What has been discovered is that gliding by M. mobile is an ATP-powered process and that M. mobile has several large ultrastructural proteins that help with surface adhesion. Because gliding is ATP powered, any proteins with ATPase functionality in the genome could be considered motility gene candidates. The metabolism of M. mobile, is like that of other mycoplasmas, but with an emphasis on protein synthesis and transport of compounds. M. mobile is able to metabolize glucose, sucrose, fructose, maltose/maltodextrin, xylose, and trehalose as energy sources. M. mobile should also be able to produce and use glycogen and starches, as can many other mycoplasma species. Fermenting of sugars appears to be the single method of producing ATP in M. mobile.

Ecology

Mycoplasma mobile is found in freshwater, discovered in the 1970s on the gills of freshwater fish hosts. There is not much other available information on how M. mobile affects the environment or in what way it is pathogenic to fish.

Pathology

M. mobile is believed to be pathogenic, adapted to living on fish hosts. The optimal growth of M. mobile occurs at around 20°C, lower than most other well-studied mycoplasmas, (around 37°C). Aside from the difference in optimal growth temperature its doubling time (10 h) is in the range of mycoplasmas with mammalian hosts. M. mobile also contains a set of repetitive elements presumed to be a variable surface antigen. A correlation of mycoplasma pathogenicity with motility implies that motility is involved in the pathogeninc process. Four antibodies have been found on the cell surface of M. mobile. Of the four, three antibodies recognized proteins from the Mvsp family. The Mvsp proteins are considered the major surface antigens of Mycoplasma mobile. The protein target of the last recognized antigen was the Gli349 protein, a protein known for its association with glass binding and movement. Gli349 is assumed to be the major protein utilized by M. mobile for adhesion to host surfaces. During experimentation, an antibody which recognized the Gli349 protein, named mAb7, was able to detach the mycoplasmas from glass. This implies that mAb7 is an inhibitory antibody which affects the gliding ability of M. mobile.

Application to Biotechnology

A unique compound produced by Mycoplasma mobile has been discovered, a nucleoside triphosphatase which serves as a very good “candidate motor for gliding ability.” The gliding ability of M. mobile is powered by ATP, but no previously isolated proteins from the organism have demonstrated that they were responsible. A 42-kDa protein named P42 has now been isolated and a study has found that P42 could be the “key ATPase in the gliding motility of M. mobile.”

Current Research

- Further research of gliding protein Gli349: Recent studies of the isolated gliding protein Gli349, in Mycoplasma mobile, have used rotary shadowing electron microscopy to help to reveal the protein’s morphology, and mechanism in gliding by binding to glass. The protein is 349-kDa, and is found at the ‘neck’ of the mycoplasma, forming spiky leg-like structures that protrude from the cell 50nm in length. This protein enables cell movement by binding and releasing, using energy obtained by ATP hydrolysis. It was found that about 60% of the protein is composed of 18 repeats of 100 amino acids. Research also showed that when inactivated, the gliding machinery could be reactivated by ATP.

- M. mobile can be used as a microtransporter and run on a set track: Because M. mobile has been found to be capable of towing particles “roughly 10 times its size, without significant loss in speed,” it has been seen as a possible microtransporter. Scientists have previously witnessed only a vigorous movement of M. mobile but had no control of their direction of movement on plain surfaces. Through the use of patterned or textured surfaces, they have now been able to control the unidirectional movement of M. mobile and have seen almost normal traveling speeds even with attached streptavidin beads. Current research is studying the possibility of using M. mobile as a microtransporter which can carry cargo around “within micrometer-scale spaces.” This is potentially very useful in medical treatments or biological systems.

- Use of M. mobile as a microrotary motor Because Mycoplasma mobile is the fastest of the mycoplasmas in gliding ability, it has been studied as a potential bio-motor. This motor would use the chemical energy of ATP and transform it into mechanical work by acting on a micro/nanotechnology scale. It has been proposed to develop “an appropriate interface between such biological materials and synthetic devices” which would put Mycoplasma mobile to use as a “hybrid micromachine.” The researchers propose developing a motor made “of a 20-µm-diameter silicon dioxide rotor driven on a silicon track by the gliding bacterium Mycoplasma mobile.” If effective, the motor could later be modified to work on a larger scale, as previously done with bacterial flagellum or pili. The motor would be more efficient than artificial motors, and would run using glucose as fuel.