Myxobacteria

Distinguish from slime molds.

Myxobacteria
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Delta Proteobacteria
Order:	Myxococcales
Families & Genera
Archangiaceae    Archangium Cystobacteraceae    Cystobacter    Melittangium    Stigmatella Myxoccaceae    Myxococcus Myxococcus xanthus    Angiococcus Polyangiaceae    Chondromyces    Nannocystis    Polyangium

The myxobacteria ("slime bacteria") are a group of bacteria that predominantly live in the soil. The myxobacteria have very large genomes, relative to other bacteria, e.g. 9-10 million nucleotides. Sorangium cellulosum has the largest known (as of 2008) bacterial genome, at 13.0 million nucleotides.^[1] Myxobacteria are included among the delta group of proteobacteria, a large taxon of Gram-negative forms.

Myxobacteria can move actively by gliding. They typically travel in swarms (also known as wolf packs), containing many cells kept together by intercellular molecular signals. This close concentration of cells may be necessary to provide a high concentration of extracellular enzymes used to digest food. Myxobacteria produce a number of biomedically and industrially useful chemicals, such as antibiotics, and export those chemicals outside of the cell.^[2]

Life cycle

When nutrients are scarce, myxobacterial cells aggregate into fruiting bodies, a process long-thought to be mediated by chemotaxis but now considered to be a function of a form of contact-mediated signaling.^[3][4] These fruiting bodies can take different shapes and colors, depending on the species. Within the fruiting bodies, cells begin as rod-shaped vegetative cells, and develop into rounded myxospores with thick cell walls. These myxospores, analogous to spores in other organisms, are meant to survive until nutrients are more plentiful. The fruiting process is thought to benefit myxobacteria by ensuring that cell growth is resumed with a group (swarm) of myxobacteria, rather than as isolated cells. Similar life cycles have developed among certain amoebae, called cellular slime moulds.

At a molecular level, initiation of fruiting body development is regulated by Pxr sRNA.^[5][6]

Clinical use

Metabolites secreted by Sorangium cellulosum known as epothilones have been noted to have antineoplastic activity. This has led to the development of analogs which mimic its activity. One such analog, known as Ixabepilone is a U.S. Food and Drug Administration approved chemotherapy agent for the treatment of metastatic breast cancer.^[7]

References

1. ^ Schneiker S et al. (2007). "Complete genome sequence of the myxobacterium Sorangium cellulosum". Nature Biotechnology 25 (11): 1281–1289. doi:10.1038/nbt1354. PMID 17965706. 
2. ^ Reichenbach H (2001). "Myxobacteria, producers of novel bioactive substances". J Ind Microbiol Biotechnol 27 (3): 149–56. doi:10.1038/sj.jim.7000025. PMID 11780785. 
3. ^ Kiskowski MA, Jiang Y, Alber MS (2004). "Role of streams in myxobacteria aggregate formation". Phys Biol 1 (3–4): 173–83. doi:10.1088/1478-3967/1/3/005. PMID 16204837. 
4. ^ Sozinova O, Jiang Y, Kaiser D, Alber M (2005). "A three-dimensional model of myxobacterial aggregation by contact-mediated interactions". Proc Natl Acad Sci USA 102 (32): 11308–12. doi:10.1073/pnas.0504259102. PMC 1183571. PMID 16061806. http://www.pnas.org/cgi/content/full/102/32/11308. 
5. ^ Yu YT, Yuan X, Velicer GJ (May 2010). "Adaptive evolution of an sRNA that controls Myxococcus development". Science 328 (5981): 993. doi:10.1126/science.1187200. PMC 3027070. PMID 20489016. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=20489016. Retrieved 2010-07-22. 
6. ^ Fiegna F, Yu YT, Kadam SV, Velicer GJ (May 2006). "Evolution of an obligate social cheater to a superior cooperator". Nature 441 (7091): 310–4. doi:10.1038/nature04677. PMID 16710413. 
7. ^ "FDA Approval for Ixabepilone". http://www.cancer.gov/cancertopics/druginfo/fda-ixabepilone.