Myxococcus

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A Microbial Biorealm page on the genus Myxococcus

"Myxococcus xanthus is a Gram-negative rod-shaped bacterium. Under starvation conditions, it undergoes a magnificent developmental process in which roughly 100,000 individual cells aggregate to form a structure called the fruiting body over the course of several hours." Courtesy of Dale Kaiser.

Classification

Higher order taxa:

Bacteria; Proteobacteria; delta/epsilon subdivisions; Deltaproteobacteria; Myxococcales; Cystobacterineae; Myxococcaceae

Species:

Myxococcus coralloides, M. flavescens, M. fulvus, M. macrosporus, M. stipitatus, M. virescens, M. xanthus

NCBI: Taxonomy Genome

Genome Structure

Myxobacterial genomes are between 9 and 10 Mbp long, larger than any free-living bacteria without a developmental cycle. They have a G+C content of between 67 and 71%. Myxococcus has a developmental cycle in which it forms multicellular fruiting bodies that contain spores. To date, no Myxobacteria genomes have been sequenced, although the genome of Myxococcus xanthus has been mapped, and measures 9.2 Mbp long with a G+C content of 67.5%.

Cell Structure and Metabolism

Myxococci are Gram-negative, spore-forming, chemoorganotrophic, obligate aerobes. They are elongated rods with rounded or tapered ends, and they are nonflagellated.

Ecology

Myxobacteria most commonly inhabit topsoil, mainly in the pH range from 5 to 8, although they can also be found at extreme pHs. They like soil rich in organic matter best, but also occur in sand and on rocky surfaces. They also inhabit decaying plant material, and are represented in fresh water. It has been shown that fruiting body formation is both possible and effective in submerged Myxobacteria. Overall, it is a rather versatile genus. Myxobacteria, due to their gliding method of motility, form colonies on agar that spread fil-like over the entire plate, after about three days, and often exhibit concentric rings.

Gliding motility, as mentioned above, is important when Myxobacteria reconvene during times of nutrient depletion in order to form fruiting bodies which consist of about 104 to 106 cells. As cells divide and multiply they move away from each other (somewhat) secreting a polysaccharide slime, which they use to retrace their steps when nutrients become scarce. They migrate back along the slime, aggregating by chemotaxis, to form fruiting bodies, which are raised above the agar surface in order to disseminate the spherical myxospores being formed by the vegetative Myxobacterial cells as they migrate upward in the fruiting body.

In addition to aggregating to form fruiting bodies, which in and of itsself, is an unusually social behavior for bacteria to exhibit, some cells also commit 'suicide' to ensure the survival of other cells. During the process of fruiting body formation only a minority of cells that aggregate form spores. Many cells, instead, lyse, releasing their contents which serve to feed the sporulating cells.

An interesting phenomenon that rises out of the aggregation of Myxobacterial cells during times of nutrient depletion, is the pattern in which they migrate. It has been observed that Myxobacteria migrate, in the early stages of starvation-induced fruiting body development, in a "highly organized periodic pattern of equispacedaccumulations that move as traveling waves" (Welch & Kaiser). There are two sets of waves, called ripples, moving in opposite directions, with the same wavelength and speed.

A field of M. xanthus traveling waves (a). Time lapse series of the traveling waves (b-e). From Welch & Kaiser.

While aggreagation for the formation of fruiting bodies during times of starvation is their most dramatic social behavior, myxobacteria exhibit other social behaviors. They move and feed in a cooperative tight group, which brings to mind a wolf-pack. They move through the soil (their natural habitat) secreting enzymes that will lyse their prey, exhibiting social predation common to much more complex organisms.

Isolation and Cultivation

Myxobacteria can be cultivated on a liquid medium containing a nitrogen source. Look up some experiments and figure it out. Get out there and have fun! Click here for an example of one recent study about finding a novel type of geosmin biosynthesis in myxobacteria.

References

Dickschat JS, Bode HB, Mahmud T, Muller R, Schulz S. "A novel type of geosmin biosynthesis in myxobacteria." The Journal of organic chemistry. 2005 Jun 24;70(13):5174-5182.

He, Qian et al. 1994. A physical map of the Myxococcus xanthus chromosome. PNAS, 91: 9584-9587.

Sporman, Alfred M. 1999. Gliding motility in bacteria: Insights for the studies of Myxococcus xanthus.

Strassman, Joan E. 2000. Bacterial cheaters. Nature, 404: 555-556.

Velicer, Gregory J. et al. 2000. Developmental cheating in the social bacterium Myxococcus xanthus. Nature, 404: 598-601.

Velicer, Gregory J. et al. 1998. Loss of social behaviors by Myxococcus xanthus during evolution in an unstructured habitat. PNAS, 95: 12376-12380.

Welch, Roy & Dale Kaiser. 2001. Cell behavior in traveling wave patterns of myxobacteria. PNAS, 98: 14907-14912.