Halobacterium salinarum- flagella

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A Microbial Biorealm page on the genus Halobacterium salinarum- flagella

Classification

Archaea; Euryarchaeota; Halobacteria; Halobacteriales; Halobacteriaceae; Halobacterium; Halobacterium salinarum

Description and significance

Formerly known as Halobacterium halobium, H. salinarum are a rod shaped, motile member of the extreme halophilic archaea. An important model organism for the study of the halophiles, they inhabit highly saline environments, at concentrations of 4M or higher. H. salinarum is capable of living in saturated salt solutions, one of the only recorded species able to thrive in these extreme environments. [4]

Genome structure

Genome consists of 1 circular chromosome and 4 megaplasmids. Chromosome has a GC content of 68 %, and plasmids have a lower GC content of 58.8%. Genome has 2878 protein-coding genes, of which 68% have been identified. [2]


Cell structure, metabolism & life cycle

Halobacterium salinarum are rod shaped, gram negative with a glycoprotein s-layer that contributes to cell integrity and maintenance of shape. Depending on the growth phase, H. salinarum are either monopolarly or bipolarly flagellated, clockwise rotation pulls the organism forward, while counter-clockwise reverses direction, pulling backward. [3,4,5] Halobacterium can grow under aerobic or anaerobic conditions, through three major pathways. H. salinarum contains the photosynthetic pigment bacteriorhodopsin, giving the organism a red/purple color and allowing the organism to survive with light as the only source of energy. Also generates ATP by the arginine fermentation pathway, or can also oxidize various compounds under aerobic conditions. [4]

Ecology (including pathogenesis)

Inhabits highly saline environments, such as the Great Salt Lake, Utah, or the Dead Sea.


Interesting feature

Although H. salinarum have a proton-driven flagella, these structures are not homologous to eukaryotic flagella. The Halobacterial flagellar filaments are about half as thick as eubacterial couterparts, and assemble differently. This makes H. salinarum an important model organism not only for investigating the extreme-halophiles, but also in understanding the evolution of this unique motility system. [4,5]


References

1. Desmond, E., Brochier-Armanet, C., and Gribaldo, S. 2007. Phylogenomics of the archaeal flagellum: rare horizontal gene

  transfer in a unique motility structure. BMC Evolutionary Biology. 7:106.

2. ExPASy Bioinformatics Information Portal. HAMAP: Halobacterium salinarum (strain ATCC 29341 / DSM 671 / R1) complete proteome.

  <http://hamap.expasy.org/proteomes/HALS3.html>. Accessed 10/20/2011. 

3. Max Planck Institute of Biochemistry. Flagella of Halobacterium salinarum and their biogenesis.

  <http://mnphys.biochem.mpg.de/en/eg/oesterhelt/web_page_list/Topic_flagella_Hasal/index.html> Accessed 10/21/2011. 

4. Max Planck Institute of Biochemistry. Halobacterium Salinarum Overview.

  <http://mnphys.biochem.mpg.de/en/eg/oesterhelt/web_page_list/Org_Hasal/index.html> 
  Accessed 10/17/2011. 

5. Strominger, J. 1976. Structural (shape-maintaining) role of the cell surface glycoprotein of Halobacterium salinarium.

  Proc. Nati Acad. Sci. 73(8):2687-2691.