MAR 23, 2016 11:02 AM PDT

Better Know a Microbe: Haloquadratum

WRITTEN BY: Kerry Evans
Haloquadratum” literally means “salt square”.

These salt-loving, square-shaped microbes are some of the most unique archaebacteria out there. Haloquadratum walsbyi was first discovered by A.E. Walsby in 1980 in the Gavish Sabkha, a hypersaline pool in Sinai used by Bedouins to collect salt. Thus, these guys are also known as “Walsby’s square archaeon”.
 
Four Haloquadratum cells line up to form a sheet.

H. walsbyi is highly abundant in salty waters worldwide, but very difficult to culture in the lab. They are likely the most halophilic organisms yet discovered, since they can grow in medium containing 2 M MgCl and 3.3 M NaCl (that’s about 10 times saltier than seawater!).

Their cells are typically 0.1 micron thick and 1.5 microns square. They form fragile, two-dimensional sheets made up of 10 cells, on average. The periphery of each cell is lined with gas vesicles that probably help H. walsbyi move through the environment.
 
Gas vesicles (GV) line the cell periphery.

So, why is it so strange for these cells to be square? In most bacteria, the cytoplasm is usually hypertonic, meaning that osmotic pressure causes cells to swell. Since H. walsbyi lives in hypersaline waters, its interior may actually by hypotonic, making the cells flat. This doesn’t really explain why the cells are square, however. Although, a related species, H. japonica, is triangular, and a specific glycoprotein helps regulate its shape. The same may be true for our square friends.
 
H. japonica are triangle-shaped.

So, they’re square and they like saltwater. Who cares? Planetary scientists do! Jupiter’s moons Europa and Ganymede are both salty, so it’s possible that halophilic organisms like Haloquadratum could be making a home there.

Sources: MicrobeWiki, Skeptic Wonder, Wikipedia
 
About the Author
  • Kerry received a doctorate in microbiology from the University of Arkansas for Medical Sciences.
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