Abstract
Microbial endolithic communities in the sandstone rocks of the southern Negev Desert, particularly in Timna Park, were initially discovered by Imre Friedmann and Roseli Ocampo-Friedmann in their pioneering study about 50 years ago. Nonetheless, this harsh microecosystem, dominated by cyanobacterial taxa, raises questions about the adaptive mechanisms that enable the survival of these microorganisms. The present study provides comprehensive data, including extensive precipitation records for the Timna Valley, and multi-year microclimatic data from a colonised site. It includes examinations of rock structure, as well as microscopic and metagenomic analysis. Our findings point to a distinct bacterial endolithic population dominated by the cyanobacterial genus Chroococcidiopsis. Although the taxa are well known, we show here how their exclusive persistence is driven by the sandstone's fine porosity and thermal properties, combined with rare, low-volume precipitation. This highly selective microenvironment highlights how specific rock and climate interactions can filter microbial diversity in hyper-arid deserts. Additionally, it demonstrates an adaptation strategy based on both short-term and decadal-scale dormancy. Thus, it offers new insights for the survival of these unique ecosystems and provides valuable perspectives for astrobiology and the search for evidence of microbial life on Mars.