Pxr sRNA

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Pxr sRNA
Secondary structure of Pxr sRNA.
Symbol Pxr
Rfam RF01812
Other data
RNA type sRNA
Domain(s) Myxococcus xanthus, Stigmatella aurantiaca

Pxr sRNA is a regulatory RNA which downregulates genes responsible for the formation of fruiting bodies in Myxococcus xanthus.[1] Fruiting bodies are aggregations of myxobacteria formed when nutrients are scarce,[2] the fruiting bodies permit a small number of the aggregated colony to transform into stress-resistant spores.[3]

Pxr exists in two forms: Pxr-L (a long form) and Pxr-S which is shorter. The short form was found to be expressed in cells during growth but is rapidly repressed during starvation. This finding implies that Pxr-S is specifically responsible for inhibiting the fruiting body development during cell growth when nutrients are abundant.[1]

Pxr homologs have only been found in one other taxon, namely Stigmatella aurantiaca. Homologs were not found in any other myxobacteria (such as Sorangium cellulosum[4] or Anaeromyxobacter dehalogenans[5]) which suggests the Pxr RNA gene may have a recent evolutionary origin in the sub-clade Myxococcales.[1]

M. Xanthus obligate cheat and phoenix phenotypes[edit]

Several mutations in the Pxr sRNA gene have been observed.[6] The first mutation causes an obligate cheat (OC) phenotype to emerge, these bacteria exploit the fruiting bodies of wild-type M. Xanthus to sporulate more efficiently. This phenotype is thought to be caused by a mutation which prevents the repression of Pxr-S, thereby inhibiting the formation of fruiting bodies indefinitely. If Pxr-S is derived from Pxr-L, it may be that RNAi-like processing elements have been knocked out.[1]

In a laboratory experiment, the OC phenotype out-competed and excluded the wild type, eventually bringing about a population crash when there were not enough wild type bacteria to exploit.[6] After this event, a new phenotype emerged via spontaneous mutation dubbed phoenix (PX).[1] The PX phenotype was developmentally superior to both OC and wt, it was able to sporulate autonomously - without forming fruiting bodies and with high efficiency.[6]


  1. ^ a b c d e 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 3027070Freely accessible. PMID 20489016. Retrieved 2010-07-22. 
  2. ^ Kuner JM, Kaiser D (July 1982). "Fruiting body morphogenesis in submerged cultures of Myxococcus xanthus". J. Bacteriol. 151 (1): 458–61. PMC 220259Freely accessible. PMID 6806248. Retrieved 2010-07-22. 
  3. ^ Wireman JW, Dworkin M (February 1977). "Developmentally induced autolysis during fruiting body formation by Myxococcus xanthus". J. Bacteriol. 129 (2): 798–802. PMC 235013Freely accessible. PMID 402359. Retrieved 2010-07-22. 
  4. ^ Schneiker S, Perlova O, Kaiser O, et al. (November 2007). "Complete genome sequence of the myxobacterium Sorangium cellulosum". Nat. Biotechnol. 25 (11): 1281–9. doi:10.1038/nbt1354. PMID 17965706. 
  5. ^ Thomas SH, Wagner RD, Arakaki AK, et al. (2008). "The mosaic genome of Anaeromyxobacter dehalogenans strain 2CP-C suggests an aerobic common ancestor to the delta-proteobacteria". PLoS ONE. 3 (5): e2103. doi:10.1371/journal.pone.0002103. PMC 2330069Freely accessible. PMID 18461135. Retrieved 2010-07-22.  open access publication - free to read
  6. ^ a b c 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. 

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