Salt deliquescence drives photosynthesis in the hyperarid A tacama D esert

Summary Endolithic cyanobacteria are found in halite nodules in the hyperarid core of the A tacama D esert. Using P ulse A mplitude M odulated F luorometry, we show here that photosynthetic systems of these cyanobacteria become active when the relative humidity rises above 70% and the salt becomes wet by way of deliquescence. This is the first evidence of active metabolism in the hyperarid core of the A tacama, and supports the view of a microbial community sustained by deliquescence. Our results expand the water activity envelope of life on E arth.