Survival of a Polyextremophilic Archaeon and Function of Its Enzyme in Potentially Astrobiological Conditions

Abstract

Haloarchaea are extremophilic microorganisms used as models for life in niche environments on Earth, Mars, and other planets. We compared growth of Halorubrum lacusprofundi, a cold-adapted isolate from Vestfold Hills, Antarctica, with Halobacterium sp. NRC-1, a mesophilic laboratory strain. Both tolerated concentrations of magnesium and perchlorate higher than expected on Mars. These Haloarchaea were exposed to and tolerated stratospheric conditions. Psychrophilic Halorubrum has a better survival rate than Halobacterium after freeze-thaw. Cold-active β-galactosidase from Halorubrum was used as a model to establish effects of inhibitory conditions. The enzyme was more inhibited by magnesium. Cold-activity of the enzyme was investigated through bioinformatics, genomics, and mutagenesis by identifying divergent amino acids and creating single amino acid mutations. Importance of the residues for cold activity was tested and confirmed using steady-state kinetics. Based on this work, Halorubrum and its enzyme are ideal models for studying adaptation in polyextreme environments on Earth and elsewhere.