Species-Specific Recognition of Mediated by UV-Inducible Pili and S-Layer Glycosylation Patterns.

The UV-inducible pili system of (Ups) mediates the formation of species-specific cellular aggregates. Within these aggregates, cells exchange DNA to repair DNA double-strand breaks via homologous recombination. Substitution of the pilin subunits UpsA and UpsB with their homologs from showed that these subunits facilitate species-specific aggregation. A region of low conservation within the UpsA homologs is primarily important for this specificity. Aggregation assays in the presence of different sugars showed the importance of -glycosylation in the recognition process. In addition, the -glycan decorating the S-layer of is different from the one of Therefore, each species seems to have developed a unique UpsA binding pocket and unique glycan composition to ensure aggregation and, consequently, also DNA exchange with cells from only the same species, which is essential for DNA repair by homologous recombination. Type IV pili can be found on the cell surface of many archaea and bacteria where they play important roles in different processes. The UV-inducible pili system of (Ups) pili from the crenarchaeal species are essential in establishing species-specific mating partners, thereby assisting in genome stability. With this work, we show that different species have specific regions in their Ups pili subunits, which allow them to interact only with cells from the same species. Additionally, different species have unique surface-layer glycosylation patterns. We propose that the unique features of each species allow the recognition of specific mating partners. This knowledge for the first time gives insights into the molecular basis of archaeal self-recognition.