Cultivation of Walsby’s square haloarchaeon

The square haloarchaea of Walsby (SHOW group) dominate hypersaline microbial communities but have not been cultured since their discovery 25 years ago. We show that natural water dilution cultures can be used to isolate members of this group and, once in pure culture, they can be grown in standard halobacterial media. Cells display a square morphology and contain gas vesicles and poly-β-hydroxybutyrate (PHB) granules. The 16S rRNA gene sequence was >99% identical to other SHOW group sequences. They prefer high salinities (23–30%), and can grow with a doubling time of 1–2 days in rich media. The ability to culture SHOW group organisms makes it possible to study, in a comprehensive way, the microbial ecology of salt lakes.