A bacterial expression cloning screen reveals single-stranded DNA-binding proteins as potent desicco-protectants

Desiccation kills most cells. Some proteins have been identified to help certain cells survive desiccation, but many protein protectants are likely to be unknown. Moreover, the mechanisms ensuring protection of key cellular components are incompletely understood. We devised an expression-cloning approach to discover further protectants. We expressed cDNA libraries from two species of tardigrades in E. coli, and we subjected the bacteria to desiccation to select for survivors. Sequencing the populations of surviving bacteria revealed enrichment of mitochondrial single-stranded DNA-binding proteins (mtSSBs) from both tardigrade species. Expression of mtSSBs in bacteria improved desiccation survival as strongly as the best tardigrade protectants known to date. We found that DNA-binding activity of mtSSBs was necessary and sufficient to improve the desiccation tolerance of bacteria. Although tardigrade mtSSBs were among the strongest protectants we found, single-stranded DNA binding proteins in general offered some protection. These results identify single-stranded DNA-binding proteins as potent desicco-protectants. [Display omitted] •Bacterial expression cloning is an effective method to identify desicco-protectant proteins•Mitochondrial single-stranded DNA-binding proteins are potent desicco-protectants in bacteria•mtSSBs promote desiccation tolerance by binding to DNA Desiccation is a harsh stress that kills most cells and organisms. Hibshman et al. used an expression-cloning approach to screen for tardigrade proteins that could improve bacterial desiccation survival. They found that mitochondrial single-stranded DNA-binding proteins can significantly improve desiccation survival—an effect that relies on their ability to bind DNA.