Halobacterium salinarum- flagella
A Microbial Biorealm page on the genus Halobacterium salinarum- flagella
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. 
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. 
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. 
Ecology (including pathogenesis)
Inhabits highly saline environments, such as the Great Salt Lake, Utah, or the Dead Sea.
Although H. salinarum use flagella to generate mobility similarly to bacteria, these structures are not homologous to eukaryotic flagella. The flagellar filaments of H. salinarum 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. [4,6] Experimental data suggests that proton-motive force may not be the only energy source for flagellar movement. Immobile H. salinarium were restored to mobility through the addition of the L-arginine, which leads to ATP production through fermentation. The use of ATP to generate flagellar force was supported when motility was found to increase in a zero proton motive force scenario through the addition of L-arginine. 
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. Streif S, Staudinger WF, Marwan W, Oesterhelt D.J. 2008. Flagellar rotation in the archaeon Halobacterium salinarum depends on ATP. Journal of Molecular Biology. 5;384(1):1-8. Epub 2008 Aug 29.
6. Strominger, J. 1976. Structural (shape-maintaining) role of the cell surface glycoprotein of Halobacterium salinarium.
Proc. Nati Acad. Sci. 73(8):2687-2691.