Walsby's square archaon has finally been isolated in pure culture, 25 years after its discovery in a pond near the Red Sea. This is a square microorganism (not a bacterium! you'd think news@Nature would get that right) found in hypersaline environments; the pure culture was isolated in medium containing 33% saline, which is about twice as salty as soy sauce. The trick was to use dilution culture to find a range of nutrient and salt concentrations in which the square archaon would out-compete contaminating species. Other square Archaea are known, but this one has eluded culture for so long, despite frequently being the dominant member of the halophile communities in which it's found, that its eventual "capture" is big news to a certain specialized group of microbiologists. Me, I just liked the pictures. Both belong to Mike Dyall-Smith, who led the group that isolated the elusive microcritter and has more information and images here. The top picture is a light microscope image (epifluorescence using acridine orange stain) and the bottom picture is an electron micrograph (bar = 1 micron, GV = gas vacuole, PHB = polyhydroxybutyrate).

Update: I forgot to mention that these things are not only square, they're very thin -- like teeny living tiles. I couldn't think why they would take that shape, so I asked Mike D-S (ain't email wonderful? I'm just some chump with a website, and I can bug a senior scientist half a world away -- and he takes time out to answer me). He says they contain bacteriorhodopsin, which is a light-driven proton pump that other Archaea use to harness the energy in sunlight. If this organism is doing the same thing, the shape makes sense as a way to maximise not only surface but also interior exposure to the sun. The gas vacuoles, then, might be a way of maintaining position at or near the water surface. (update 041018, stupid error fixed: s/photon/proton)