A variant of the hyperthermophile Archaeoglobus fulgidus adapted to grow at high salinity

A variant of Archaeoglobus fulgidus VC-16 was isolated from cultures obtained after a stepwise transfer from media containing 1.8-6.3% NaCl by a plating-independent, selected-cell cultivation technique, using a laser microscope. This variant, A. fulgidus VC-16S, had a higher growth rate throughout the salt range of the parental strain, but was also able to grow in media containing NaCl up to 6.3%, whereas the parental strain could not grow above 4.5% NaCl. Diglycerol phosphate (DGP), only encountered in the Archaeoglobales, was the major solute accumulated under supra-optimal salinities, whereas at supra-optimal growth temperatures di-myo-inositol phosphate was the predominant solute. The accumulation of compatible solutes during growth of variant VC-16S was lower than in the parental strain within 1.8-4.5% NaCl, but the levels of compatible solutes, including DGP, increased sharply in the variant at higher salinities (5.5 and 6.0%). This variant represents, at this time, one of the most halophilic hyperthermophiles known, and its ability to grow at high salinity appears to be due to the massive accumulation of DGP.