Thrive or survive: prokaryotic life in hypersaline soils

Abstract

Background Soil services are central to life on the planet, with microorganisms as their main drivers. Thus, the evalu‑ ation of soil quality requires an understanding of the principles and factors governing microbial dynamics within it. High salt content is a constraint for life afecting more than 900 million hectares of land, a number predicted to rise at an alarming rate due to changing climate. Nevertheless, little is known about how microbial life unfolds in these habitats. In this study, DNA stable-isotope probing (DNA-SIP) with 18O-water was used to determine for the frst time the taxa able to grow in hypersaline soil samples (ECe=97.02 dS/m). We further evaluated the role of light on prokary‑ otes growth in this habitat. Results We detected growth of both archaea and bacteria, with taxon-specifc growth patterns providing insights into the drivers of success in saline soils. Phylotypes related to extreme halophiles, including haloarchaea and Salinibacter, which share an energetically efcient mechanism for salt adaptation (salt-in strategy), dominated the active community. Bacteria related to moderately halophilic and halotolerant taxa, such as Staphylococcus, Aliifodinibius, Bradymonadales or Chitinophagales also grew during the incubations, but they incorporated less heavy isotope. Light did not stimulate prokaryotic photosynthesis but instead restricted the growth of most bacteria and reduced the diversity of archaea that grew. Conclusions The results of this study suggest that life in saline soils is energetically expensive and that soil hetero‑ geneity and traits such as exopolysaccharide production or predation may support growth in hypersaline soils. The contribution of phototrophy to supporting the heterotrophic community in saline soils remains unclear. This study paves the way toward a more comprehensive understanding of the functioning of these environments, which is fundamental to their management. Furthermore, it illustrates the potential of further research in saline soils to deepen our understanding of the efect of salinity on microbial communities.